Canine obesity is associated with comorbidities, a shortened lifespan, and a poorer quality of life, but epidemiological studies characterizing canine obesity in Latin America are scarce. Therefore, this study aimed to determine the prevalence of canine obesity in the city of Sao Paulo, Brazil, and the possible associated causal factors. Randomly-selected households from different city regions were visited. Dogs in each household were evaluated and owners completed a questionnaire whilst their anthropometric measures were taken. Total of 285 dogs from 221 owners were included, and the combined prevalence of overweight and obesity was 40.5%. The prevalence of overweight and obesity was greater in female dogs (P = 0.003) and in dogs that were neutered (P = 0.001). There was also a positive association between BCS and frequency of visits to a veterinarian (P = 0.026), feeding frequency (P = 0.033), and higher snack intake (P = 0.011). Further, the BCS of dogs was greater when their owners reported consuming more snacks themselves (P = 0.005) and whose had a presence of elderly people in the household (P = 0.006). In conclusion, the prevalence of obesity found in a Brazilian metropolitan region was similar to that if other countries, and neutering and snack intake were associated with the development of this disease.