The leopard grouper Mycteroperca rosacea is endemic to northwestern Mexico. It has been classified as vulnerable by the IUCN since 2008. M. rosacea has high commercial value and is caught yearround in Baja California Sur (BCS). Biological information on this species, especially in its natural environment, is scarce, and the objective of this study was to analyze its reproductive biology in Santa Rosalía, BCS. A total of 345 specimens were collected from March 2014 to May 2015. The sex ratio was 2.0: 1.0 (females: males, P < 0.05). Population size at first maturity (L50) was estimated at 40.77 cm TL; 37.31 cm TL for males and 42.44 cm TL for females. Gonadic development was synchronous by group, with a reproductive period occurring from March to May in 2014 and 2015 (at 20-23ºC). The gonadosomatic index achieved maximum values in May 2014 and March 2015, as did the highest frequencies of mature and spawning individuals, indicating that there was a clear seasonal pattern of reproduction, and a negative correlation with temperature for both sexes. The hepatosomatic index and the condition index indicated that M. rosacea is not a species that requires storing of energy for reproductive events, as it seems to have food available year-round.The leopard grouper Mycteroperca rosacea is endemic to northwestern Mexico. It has been classified as vulnerable by the IUCN since 2008. M. rosacea has high commercial value and is caught year-round in Baja California Sur. Biological information of this species, especially in its natural environment, is scarce, and the objective of this study was to analyze its reproductive biology in Santa Rosalía, BCS. A total of 345 specimens were collected from March 2014 to May 2015. The sex ratio was 2.0: 1.0 (females: males, P