This paper describes the characteristics of male and female germ cells during gonadal development and the gonadal maturity scale of the blue crab, Callinectes sapidus. A total of 20 specimens were collected monthly from June to November 2012, in two areas off the coast of the Gulf of Mexico: the San Andrés Lagoon and Alvarado Lagoon. The gonads were removed and processed following the standard technique of hematoxylin and eosin staining. An important event in oogenesis (pre-vitellogenesis) was the appearance of a perinuclear vesicle in the cytoplasm and the accumulation of yolk granules. Later, vitellogenesis began and there was an accumulation of nutritive droplets and fragmentation of the perinuclear vesicle. During spermatogenesis, the accumulation of two fluids was observed that were involved in the formation of the spermatophore and the delay of spermiogenesis. Based on the histological features of gonad maturity, five stages were described (inactive, early gametogenesis, development, maturity, and resorption), in females and males. This proposal can be useful for the study of reproductive seasonality of this species.