Chironius bicarinatus is a common colubrid snake, widely distributed throughout the Atlantic Forest. Field observations of copulation and combat, combined with data on preserved and captive snakes, as well as on specimens brought to Institute Butantan provided a better characterization of the reproductive cycle of this species. Chironius bicarinatus has a seasonal reproductive cycle with extended vitellogenesis and ovulation, and oviposition occurring at the onset of the rainy season (austral spring). Recruitment of newborns occurred mainly at the end of the rainy season. Clutch size ranged from five to 14 and relative clutch size ranged from 0.55 to 0.62. Copulation was observed four times, always in April (austral autumn) at the onset of vitellogenesis. These records correspond to the activity peak of males in the field. Thus, mating may occur prior to ovulation (in austral spring) indicating a dissociated reproductive pattern. We suggest that combat in November (in austral spring), recorded in a previous study, may be related to the presence of androgens in snakes during the non-mating season.