Stock assessment and reproductive biology of the blue swimming crab, Portunus pelagicus, in Bandar Abbas coastal waters was conducted from August 2006 to July 2007. A total of 424 male and 348 female crabs were taken to the laboratory for length, weight and reproductive biometry. Estimate of growth parameter of crab showed t asymptotic carapace width (CW) was 172.5 mm, the curvature parameter, K(year-1) was 0.98, total mortality coefficient, Z(year-1) was 2.13, natural mortality coefficient, M (year-1) was 1.05 and the fishing mortality coefficient, F(year-1) was 1.08 then the exploitation rate, E (year-1) was 0.51. Results showed the sex ratio was 1:1.2 with 46.1% female throughout the year. All four stages of ovarian development were observed throughout the year. The Gonad Somatic Index (GSI) monthly mean values ranged between 2.05 to 2.97%. The highest values of GSI were recorded in December. Carapace width of ovigerous crabs varied from 32 to 173 mm. This crab spawned all year round with a spawning peak in December. The fecundity of ovigerous crabs ranged from 277421 to 1114348 eggs, with average fecundity of 662978 eggs. The minimum carapace width (CW) of sexually matured female crabs was 32-151 mm.