Bothrops moojeni inhabits riparian forests and adjacent open, wet areas in the Brazilian Cerrado. We address several aspects of the reproductive biology of a population from southeastern Brazil, including sexual maturation and dimorphism, male and female reproductive cycles, and sperm storage. We also provide the first record of male-male combat behavior in the wild. We sampled specimens held in the scientific collection of the Butantan Institute, São Paulo, Brazil. After macroscopic analyses and dissections, we collected the testes of males and the posterior uterus of females showing uterine muscular twisting for microscopic analyses. Males < 54.5 cm and females < 58.0 cm were sexually immature. Mature females are larger than males, although male-male combat is reported for this species. Male-male fighting and copulation occur during late summer in the wild. Histological analysis of the testes confirmed that sperm production occurs simultaneously with those reproductive events. Females showed an extended period of vitellogenesis, from February to November (late summer to spring). We observed stored sperm in the female reproductive tract during autumn. Because mating is not synchronous with ovulation, sperm storage is an obligatory component of the reproductive cycle of B. moojeni. Ovulation begins in August (winter) but most females with the presence of embryos in the oviducts occurred from January to March (summer). Parturition in captivity occurred in February, confirming that births are concentrated in the summer. Given that the Cerrado is highly fragmented in southeastern Brazil, studies on the reproductive biology of additional B. moojeni populations might provide useful information regarding intraspecific variation in reproduction in pit vipers.