Abstract Rhipicephalus sanguineus ticks are distributed throughout the world, especially in those areas in which dogs are in close contact with humans. R. sanguineus and fleas are regarded as the main ectoparasites infesting dogs in Brazil. Besides causing direct damage during the blood feeding process, this tick species can also transmit pathogens to dogs and humans. Despite its importance in Brazil, data regarding the seasonality of R. sanguineus are limited, especially with regard to natural infestations of dogs. The present study aimed to evaluate the seasonality of R. sanguineus on dogs living in Belo Horizonte, state of Minas Gerais. From August 2006 to July 2007, ticks were collected monthly from 12 adult dogs in nine houses, which were located in two districts in the north region of the city. In parallel, canine clients of a pet care department of the small animal veterinary clinic were examined for the presence of ticks before bathing and/or clipping. The climatic data recorded for Belo Horizonte during the experimental period were: mean temperature 18.6 °C; relative air humidity 56.5%; rainfall 37 mm. The only species of ticks identified from all infested dogs was R. sanguineus, which was found in all its development stages. Among dogs living in houses, three tick population peaks were observed (August, February, and June), suggesting the occurrence of three generations per year in Belo Horizonte. A total of 7318 ticks were collected, of which 5422 were adult ticks and 1896 represented immature stages (744 larvae and 1152 nymphs). The monthly inspection of dogs living in houses demonstrated significantly higher parasitism during the dry season ( p < 0.05). A total of 2848 dogs from the pet care department of the small animal veterinary clinic were examined, of which 222 (7.8%) were infested with ticks and the percentage of infested dogs in the dry season was higher ( p < 0.05) than in the hot wet. The percentage of male dogs infested with ticks was significantly higher (58.29%) than the percentage of infested female dogs (41.70%). This study of the dynamics of R. sanguineus infestations in Belo Horizonte will contribute to establishing appropriate measures to control tick infestations in dogs.