In total, 1500 specimens (448 males and 1052 females) of the flea Ctenocephalides felis felis (Bouché (Siphonaptera: Pulicidae) were collected over a period of a year from 150 dogs captured by the Centro de Controle de Zoonoses de Belo Horizonte, Minas Gerais, Brazil. Microscopic examination of the dissected fleas revealed that 180 fleas were infected with a species of gregarine that was subsequently identified as a member of the genus Steinina. The relative abundances, prevalence rates, and seasonal variation of the different developmental stages of this endoparasite in C. felis felis were determined. Both gamonts and gametocysts presented significant seasonal variation.