Massachusetts Dog Laws: Bites, Dangerous Dogs, and Penalties

Massachusetts dog laws require you to license your dog, keep its rabies vaccination current, follow state and local restraint rules, and accept strict liability if your dog injures a person or their property. Chapter 140 of the General Laws sets the framework, and violations range from a $50 ticket for a minor control offense up to 90 days in jail for ignoring a dangerous dog order. What follows walks through each obligation, the penalties for falling short, and the defenses that can apply when a bite or complaint reaches a hearing.

Licensing and Vaccination

If you own or keep a dog older than six months, you must get a license from the city or town where the dog lives.¹ You apply through your local licensing authority, usually the town clerk, and the office will not issue the license without a veterinarian’s certificate showing a current rabies vaccination or documentation that the dog is medically exempt.

License fees are set by the municipality, not the state. Most towns charge somewhere between $10 and $25, with spayed or neutered dogs costing a few dollars less. Chelmsford, for example, charges $20 for a fixed dog and $25 for an intact one. Miss the annual renewal deadline and you’ll pay a late fee on top.

Four or more dogs means you need a kennel license instead of individual licenses. Kennel fees are set by state law: $10 for up to four dogs, $25 for five to ten, and $50 for more than ten.² Dogs under six months old don’t count toward the total.

Every dog six months or older must be vaccinated against rabies by a licensed veterinarian.³ After the initial shot, revaccination follows the manufacturer’s schedule, typically every one to three years. Your veterinarian issues a certificate and a tag at each visit, and the tag has to be attached to the dog’s collar or harness. Bring a dog into Massachusetts from another state and it must be vaccinated within 30 days of arrival or upon reaching six months old, whichever comes later. Without a current rabies certificate, you can’t license the dog, and that gap exposes you to additional penalties.

Leash and Restraint Rules

There is no single statewide leash law that applies everywhere at all times. The state licensing law conditions every dog license on the dog being “controlled and restrained from killing, chasing, or harassing livestock or fowl.”¹ Beyond that baseline, a mayor or board of selectmen can issue an order requiring all dogs to be restrained from running at large during specified times.⁴

Chapter 140, Section 173 also lets every city and town pass its own ordinances or bylaws governing the control of animals.⁵ Most municipalities use that authority to require leashes in public spaces, and many cap leash length at six feet. What counts as “controlled” in a rural field may be voice command; on a city sidewalk it will almost always be a physical leash. Check your own town’s rules.

If your municipality has issued a restraint order and your dog is found running loose, an officer can hold the dog for up to seven days. Reclaiming it costs $40 for each day it was held.

Strict Liability for Dog Bites

Massachusetts is a strict liability state. If your dog injures a person or damages their property, you are liable regardless of whether you knew the dog was aggressive or whether you took precautions.⁶ There is no “one free bite” rule. The moment the dog causes harm, the law holds you responsible for the full extent of the damages.

If the dog’s owner is a minor, the parent or guardian carries the liability instead. Compared to states where a victim must prove the owner knew the dog was dangerous, Massachusetts skips that step entirely.

The statute recognizes three defenses. You are not liable if the injured person was trespassing, committing another wrongful act on your property, or teasing, tormenting, or abusing the dog at the time of the injury. For children under seven, the law presumes the child was not trespassing or provoking the dog, and the burden shifts to you to prove otherwise.⁶ That presumption makes bite claims involving young children very hard to defend.

Dangerous Dog Classifications

A “dangerous dog” is one that either attacks a person or domestic animal without justification and causes injury or death, or behaves in a way a reasonable person would consider an unjustified imminent threat of injury or death.⁷ A lesser “nuisance dog” category covers problems like excessive barking or minor disturbances.

The statute rules out three grounds for a dangerous classification: growling or barking alone, breed, and reactions proportionate to provocation.⁸ Massachusetts has rejected breed-specific bans at the state level.

Anyone can file a written complaint with the local hearing authority. The authority investigates, holds a public hearing where the complainant testifies under oath, and can dismiss the complaint, classify the dog as a nuisance, or classify it as dangerous. The hearing considers whether the dog was defending itself, its offspring, or a person; whether the person bitten was committing a crime on the owner’s property; whether the person was provoking the dog; or whether the person had broken into an area where the dog was kept away from the public. The same under-seven presumption applies.

Orders the Hearing Authority Can Impose

If your dog is classified as dangerous, the hearing authority must order one or more of the following:

Humane restraint that does not involve chaining or tethering to a stationary object.
Confinement on your property, either securely indoors or in a locked outdoor pen with a secure roof and sides embedded at least two feet into the ground.
A muzzle and a chain or tether rated for at least 300 pounds tensile strength and no longer than three feet whenever the dog is off your premises.
Liability insurance of at least $100,000 covering injuries or property damage caused by the dog, or proof of reasonable efforts to obtain it.
Permanent identification such as microchipping, tattooing, or photographs.
Spay or neuter unless a veterinarian certifies the dog is medically unfit for the procedure.
Humane euthanasia in the most serious cases.

These are minimums, and the hearing authority can combine them.⁸ You also cannot sell, transfer, or give away a dog with a dangerous classification without telling the new owner about the finding.⁹

Fines and Criminal Penalties

Where a municipality has not set its own fine schedule, the state defaults apply. You have 21 days to pay a dog control violation ticket. Within a single year, the default fines are:

First offense: dismissed with no fine.
Second offense: $50.
Third offense: $60.
Fourth or subsequent offenses: $100.

Local fines may be higher or lower.¹⁰ Ask your town clerk or animal control officer for the schedule that applies where you live.

A dog seized under a restraint order is held for up to seven days, and you pay $40 per day to reclaim it.⁴ If you have already received notice that your dog caused damage to someone’s property and still fail to keep it restrained, the fine is at least $25, and an officer can euthanize the dog if it’s found off your property without supervision.

Ignoring a dangerous dog order is a criminal offense. A first violation carries a fine of up to $500, up to 60 days in jail, or both. A second or subsequent violation increases the maximum fine to $1,000 and the maximum jail time to 90 days.⁹

Defenses Available to Owners

The defenses depend on the type of proceeding. In a Section 155 bite claim, the three recognized defenses are that the injured person was trespassing, committing some other wrongful act, or actively provoking the dog.⁶ For a victim under seven, the presumption cuts against you unless you can prove otherwise.

In dangerous dog hearings, the defenses are broader. A dog cannot be classified as dangerous if it was protecting itself, its puppies, another pet, or a person from an attack. The same applies if the person bitten was committing a crime on the owner’s property, was provoking the dog, or had broken into an enclosed area where the dog was kept away from the public. The dog’s reaction must also be “grossly disproportionate” to the circumstances for a dangerous classification to stick.⁸ A dog that snaps at someone climbing your fence stands in a very different position than one that chases a jogger down the street.

Service Animals Are Treated Differently

Federal law layers on top of state dog law for service and assistance animals, so the ordinary rules don’t map cleanly. Under the Americans with Disabilities Act, a service animal is a dog individually trained to perform a specific task for a person with a disability, such as guiding someone who is blind, alerting someone who is deaf, or calming a person during a PTSD episode.¹¹ Dogs that provide only emotional comfort without a trained task do not qualify as service animals under the ADA.

Business staff can ask only two questions: whether the dog is a service animal required because of a disability, and what task it has been trained to perform. They cannot demand documentation, ask about the disability, or require the dog to demonstrate its task.¹² Housing works differently again: under the Fair Housing Act, landlords must make reasonable accommodations for assistance animals, a broader category that includes emotional support animals, and cannot charge a pet deposit or pet fee for one.¹³

1
General Court of Massachusetts. Massachusetts General Laws Chapter 140, Section 137 – Dog Licensing
2
General Court of Massachusetts. Massachusetts General Laws Chapter 140, Section 137A – Kennel Licenses
3
General Court of Massachusetts. Massachusetts General Laws Chapter 140, Section 145B – Rabies Vaccination
4
Mass.gov. Animal Laws and Regulations in Massachusetts, 2025 Edition
5
General Court of Massachusetts. Massachusetts General Laws Chapter 140, Section 173 – Ordinances and By-Laws Relating to Animals
6
General Court of Massachusetts. Massachusetts General Laws Chapter 140, Section 155 – Damage by Dogs
7
General Court of Massachusetts. Massachusetts General Laws Chapter 140, Section 136A – Definitions
8
General Court of Massachusetts. Massachusetts General Laws Chapter 140, Section 157 – Nuisance and Dangerous Dogs
9
General Court of Massachusetts. Massachusetts General Laws Chapter 140, Section 157A – Non-Compliance With Dangerous Dog Order
10
Mass.gov. Pay a Dog Control Violation Ticket
11
ADA.gov. ADA Requirements: Service Animals
12
ADA.gov. Frequently Asked Questions About Service Animals and the ADA
13
U.S. Department of Housing and Urban Development. Fact Sheet on HUD’s Assistance Animals Notice