Luis Arroyo was sentenced to seven years in prison after pleading guilty to mistreatment of an animal and domestic abuse.
The 40-year-old attacked the two-month-old Chihuahua puppy and punched his girlfriend in the western mountain town of Lares on 4 February.
Judge Carlos Lopez Jimenez also fined Arroyo $3,000 (Â£2,400) in the case.
According to El Vocero newspaper, jobless Arroyo had been living with his 38-year-old girlfriend for six months.
The puppy died instantly, the daily reports.
No motive was given for the attack.
A man in the US territory of Puerto Rico has been jailed for biting the head off his girlfriend's dog.