Clasper gland morphology and development in Potamotrygon magdalenae and its relation with the acquisition of reproductive maturity is described in males of different developmental stages (embryos, neonates, juveniles, and reproductively active and resting adults). The glands are subcutaneous masses in the proximal base of each clasper. They are partially bilobate organs with a ventral groove that bears a row of papillae. Glands tend to be asymmetric, the left gland has a larger size, a trend that has been observed in other organs of elasmobranchs. Glands are formed by radially organized tubular secretory units lined with a simple columnar epithelium with basal nuclei and granular eosinophilic cytoplasm; vascularized loose connective tissue surrounds the gland units. The gland is covered by two layers of striated muscle tissue in circular and longitudinal arrangement. The clasper glands begin to develop in neonates and their secretory activity begins in juveniles. The active secretion of the clasper gland is observed in mature males, it includes glycoproteins and sulfated mucopolysaccharides. The size of the glands has a positive and direct relationship with body size, measured as disc width. Significant differences in clasper gland size were found between mature (active and resting) and immature (neonates and juveniles) males, suggesting that the acquisition of the sexual maturity involves the increase in the size of the gland due to a highly augmented secretory activity. Therefore, clasper glands are clearly associated with the reproductive activity of males and their secretion should have an endocrine control as other sexual secondary organs. J. Morphol. 278:369-379, 2017. © 2017 Wiley Periodicals, Inc.