The present study aimed to investigate the histological structure of testis as an important organ of the reproductionon and survival in the male blue swimming crab Portunus segnis in the Persian Gulf. In this regard, 20 male blue swimming crabs with average weight of 229.09± 15.17 gr caught from the coasts of Hendijan in Khuzestan Province from September to June, 2016. After anesthesia and morphological examination, samples were stained with Hematoxylin and Eosin method. Based on the results, testis was surrounded by connective tissue. The connective tissue lamellae divide testicular parenchyma into a number of specific lobules. Testis lobules have a Germinal Zone and a Transformation Zone. Vas deferens has anterior, medial and posterior portions. The three portions of vas deferens are surrounded externally by connective tissue and internally by cuboidal and culomnar epithelium. Spermatophores with circular to oval shapes of various sizes were observed in all three portions of vas deferens. Averages diameter of spermatophores were measured 167.64±26.38 µm.