The reproductive cycle, stages of gonadal development, and minimum size of sexual maturity are described for a population of the clam Donax punctatostriatus Hanley, 1843 from a sandy beach in southern Sinaloa, Mexico. A total of 880 clams were collected from January 2009 to June 2010; 3.2% were sexually undifferentiated and 1.4% had the trematode parasite Postmonorchis sp, in the gonadal tissue. The total length of the clams ranged from 3.5–25.64 mm ( = 13.51, S.D. = ±4.47 mm). The sexual proportion did not differ significantly from ♀1:1♂ (p > 0.05). The minimum size at sexual maturity (L₅₀) was L₅₀ = 12.03 mm. The gametogenic cycle comprise six stages of gonadal development (0-V). The population is reproductively active throughout the year and spawning is continuous, with three major peaks in April, July and September 2009. In March, when the water temperature was between 21–23 °C, most individuals were in stage I. This period is characterized by a rapid maturation of gametes. At the end of October and during November, when water temperature was warmer (25–28 °C), 50% of the individuals were in stage V (spent). Recruitment was more intense from July to October of 2009, when the highest temperatures of the year were recorded (28–31 °C). Photoperiod and the proportion of mature individuals of both sexes were significantly correlated (Pearson's correlation value = 0.62; p < 0.05). Since this clam is a potential resource for human consumption, the information here presented may contribute to a better management and use of their populations in the Mexican Pacific.