In this paper, the fecundity in Macrobrachium acanthurus (Wiegmann, 1836) of the Ribeira de Iguape river (Southern Brazil) (Crustacea, Decapoda, Palaemonidae), is presented. The mean individual fecundity of the population was estimated. Fecundity was related to either length and/or weight. Our data showed that this species presents high fecundity and is thus suitable for comercial culture. The fecundity/length and fecundity/weight relationships obtained are: F = - 14 712 + 2 311,8 L and F = -1493,9 + 798,76 W