In this study, some reproductive characteristics (reproductive season, first maturation size (LM50) and sex ratio) of the jinga shrimp, Metapenaeus affinis (H. Milne Edwards, 1837), in Izmir Bay (Aegean Sea, Turkey) were investigated. A total of 2894 M affinis were obtained from commercial fishermen between November 2008 and January 2011. The total length and weight of the females or males were measured as 7.3-17.5 cm and 2.6-38.9 g or 7.8-15.4 cm and 2.6-41.6 g, respectively. The samples were composed of 56.6% females and 46.6% males, with a female to male ratio of 10.77. The spawning period was determined from May to October. The total lengths at first maturity of females and males were 10.64 cm and 10.16 cm, respectively.