The reproductive characteristics of crabs play an important role in their fisheries management. The blue swimming crab Portunus pelagicus is one of the most commercially important crustaceans distributed along the Egyptian Coast; it has a great demand for their esteemed food. The spawning season of P. pelagicus was estimated based on three parameters: the monthly variation in both the maturity stages and in the gonado-somatic index (GSI) beside the histological examination of the ovarian structure. P. pelagicus was capable of continuous spawning throughout the year, where the mature stage was found to be distributed along the whole year indicating that crabs may be spawn at different times. P. pelagicus spawning mainly takes place twice, January-February (winter period) and June- August (summer period). As the monthly variation in GSI exhibit two distinct peaks in winter and summer. The mean size at which P. pelagicus became potentially reproductive (L_m50) was estimated to be 9.32 cm CW for males and 8.45 cm CW for females. To achieve the sustainable utilization, it is recommended to increase the minimum fishing size of this crab to at least 11.0 cm CW to protect the stock biomass and allow young individuals to reach the suitable marketable size.