The importance of decapod crustaceans has induced scientific studies in various fields of biology. Therefore, structure, reproductive biology and fecundity of a population of Potimirim brasiliana Villalobos, 1959 from Jureia-Itatins Ecological Station in Peruibe, State of Sao Paulo, were studied. Shrimps were captured at 4-month intervals from spring 2000 to summer 2001. Overall sex ratio was skewed towards males (2.2 males : 1 female). Mean +/- S.D. total body length was 17.1 +/- 2.1 mm (or 4.8 mm carapace length (CL)) for females and 14.0 +/- 1.4 mm (or 3.6 mm CL) for males. Ovigerous females comprised 55.4% of all females collected and were present in all samples and at higher proportions in the spring and the summer. The size at onset of maturity (= smallest ovigerous female) was 13.3 mm (CL = 3.7 mm). Fecundity ranged from 171 to 749 eggs (mean +/- S.D. = 361.5 +/- 119.5 eggs) per female. In addition, there was a positive correlation between the number of eggs and the carapace length of ovigerous females according to the equation NE = 197.99CL - 520.75. Mean +/- S.D. size and volume of eggs was 520.1 +/- 32.5 x 309.1 +/- 17.8 mu m and 0.038 +/- 0.006 mm(3) (early eggs) and 534.2 +/- 15.8 x 324.4 +/- 12.6 mu m and 0.042 +/- 0.003 mm(3) (late eggs). The increment in size during the embryonic development was marginally significant for the minor axis (U = 3; p < 0.047), not significant for the major axis (U = 5; p=0.117) and significant for volume (U = 840; p=0.0009). Compiled data on the reproductive pattern reported for Potimirim Holthuis, 1954 species from Brazil revealed that temporal variation of reproductive activity and fecundity are influenced by environmental limiting factors correlated with latitude.