This study provides a detailed description of the macro- and microscopic anatomy of the male reproductive system and the spermatogenesis of the mangrove land crab, Ucides cordatus. A total of 64 adult males were collected between December 2002 and February 2005 in mangroves of the Baía de Antonina, State of Paraná, Southern Brazil (25°25′08″S, 48°42′33″W). The reproductive system of this species is composed of the following paired symmetrical structures: testes, vasa deferentia (distal, medial and proximal portions), ejaculatory ducts and penises. During spermatogenesis, which takes place in the testes, the following developmental stages are observed: primary and secondary spermatogonia, primary and secondary spermatocytes, spermatids and spermatozoids. Production of male gametes was continuous throughout the study period, indicating that males of this species are physiologically capable of reproducing all year long.