Animal control officers confiscated about 1,000 rats from the home of a 67-year-old man who they said was living in filthy conditions with the animals.
Some of the rats were running loose in the home, while others were caged, officials said.
Roger Dier, who lives at the Petaluma home, was issued a misdemeanor citation. The case is being investigated by the city's Animal Services department and the Sonoma County Environmental Health Division.
The rats were transported to the city's animal shelter in cages acquired from local pet shops.
In 2001, police arrested the Petaluma "cat woman," a former San Francisco real estate agent who was found with hundreds of cats crowded into a house she owned. Some of those animals were dead and others were sick or injured, authorities said.