The mako shark is an important target for commercial and sport fishing on the south-western coast of Baja California, but few biological studies have been carried out on this species in Mexico. A sample of 301 individuals (153 females and 148 males) was collected from the landings of traditional fisheries. The size of the specimens ranged from 69 cm to 290 cm TL. The sex ratio was 1.03/1. The males were found in three stages of maturity: immature, sub-adult and mature, while the females in only the first two stages. Male mako sharks mature at about 180 cm TL. They showed radial type spermatocyst development, of which seven stages were differentiated. Females showed an internal type ovary, and only three differentiated stages of ovarian follicle development. As many sharks caught were juveniles or neonates, it is suggested that the south-western coast of Baja California represents a nursery area for the mako shark.