The aim of the present work was to study the reproductive behavior of the mangrove crab (Ucides cordatus) in the estuary of the Igaraçú River (Piauí, Brazil). Courtship and mating were observed in December 2007 and in January-March 2009. The most frequently observed reproductive behavior was the transference of eggs onto the abdomen of the female. Some disputes between males and some copulations were observed. The males mated with more than one female each night and all mating activity occurred at night. The establishment of a closed season coinciding with the mating season represented an effective strategy for the preservation of the species when the socioeconomic situation of the community of gatherers was taken into account.