In this study, histological characterization of male gonad of wels, Silurus glanis, were investigated over a period of one year in Anzali Wetland. The testes of 196 male specimens that were caught in different sizes by traps were fixed in Bouin’s solution. Then samples were prepared by classical methods of histology with Hematoxylin and Eosin (H & E) staining and studied by light microscope. Also, the gonadosomatic index (GSI %) were determined during the sampling period.  Six testicular maturation stages were observed including: immature (I), early developing (II), late developing (III), ripe testes (IV), running ripe testes (V) and spent (VI). Spermatogenesis was done during a relatively long period of one year. The stages IV and V and sperm production were occurred from late February to early June and stage VI was from June to early August. The maximum mean value of GSI% were due to late May and early June. This index decreased clearly in July. The results showed that spermiation was started in late June and resumed to late August.