Massachusetts dog laws: leash, licensing, bites and breed rules

This is a general summary of Massachusetts state law for dog owners. It is information, not legal advice. Reviewed November 2026.

Leashes and licensing

The statutes cited here do not set a statewide leash rule. They let a city or town adopt additional ordinances and by-laws on licensing and control of animals (M.G.L. c. 140, s. 173), so leash and at-large rules are local.

Licensing is a state requirement run locally. An owner or keeper of a dog over 6 months must license it with the licensing authority in the city or town where the dog is kept, and the town may not grant the licence without a veterinarian's certificate of rabies vaccination or an exemption (c. 140, s. 137).

Rabies vaccination

Each owner or keeper of a dog 6 months or older must have it vaccinated against rabies by a licensed veterinarian and revaccinated at the manufacturer's intervals. A violation carries a fine of up to $100 (c. 140, s. 145B).

When a dog bites a person, state rabies protocol calls for a 10-day quarantine that the local animal control officer or inspector orders. It is often served at the owner's home if the home is escape-proof.

Dangerous dogs and bites

Massachusetts makes the owner or keeper liable for any damage a dog does to a person's body or property, unless the person was trespassing or committing another tort, or teasing, tormenting or abusing the dog. If the injured minor is under 7, the law presumes none of those exceptions applies (c. 140, s. 155).

Any person can file a written complaint with a city or town hearing authority that a dog is a nuisance dog or a dangerous dog. A dog is not dangerous solely for growling or barking, or based on its breed, and the law excuses dogs reacting to an attack, a crime on the owner's property, or provocation. For a dangerous dog, the hearing authority orders one or more steps: restraint, secure confinement, a muzzle and short heavy leash off the premises, $100,000 in insurance, identification, neutering, or humane euthanasia. The owner can seek review in district court within 10 days (c. 140, s. 157).

Breed-specific rules

Breed cannot be the basis for a dangerous-dog finding, and the same section says no city or town shall regulate dogs in a manner that is specific to breed (c. 140, s. 157).

Tethering and hot cars

The tethering law is detailed. A dog may not be chained or tethered for longer than 5 hours in 24, or outside from 10 p.m. to 6 a.m., unless the tethering lasts no more than 15 minutes and the dog is attended. The tether may not let the dog leave the property or weigh more than 1/8 of the dog's weight, and a dog under 6 months may not be tethered outside at all. Hand-held leash walking is not covered. A dog may not be left outside during a weather advisory or in extreme weather (c. 140, s. 174E).

Confining an animal in a vehicle where heat or cold could threaten its health is a civil infraction, with fines of up to $150, then $300, then $500 for repeat offences. Officers and firefighters may enter to protect the animal. A bystander may enter only after trying to find the owner, calling 911 or law enforcement first, finding the vehicle locked, using no more force than reasonably necessary, believing the animal is in imminent danger and staying nearby until help arrives, and is then immune from liability (c. 140, s. 174F).

Where to check your local rule

Cities and towns often set stricter leash, licence and number-of-dogs rules. Check the town clerk, animal control or the town by-laws. If a dog has bitten someone or been reported, talk to a lawyer or the animal-control office.