In the present research, the histology of the testes of Nile tilapia were done on 56 males sexually mature Nile tilapia fish collected monthly from the River Nile at Giza over the period from September 2009 to August 2010. The testis of the Nile tilapia during the spring, summer and autumn seasons was surrounded by very thin tunica albuginea. The testicular capsule extended inside the testis to give connective tissue septa. The bulk of the testis was composed of seminiferous tubules. These tubules were surrounded by interstitium. The tubules filled with germinal cysts; contained germinal cells at different stages of development and surrounded by cytoplasmic processes of Sertoli cells. The spermatogenic cells were spermatogonia type A and type B, primary spermatocytes, secondary spermatocytes, spermatids and spermatozoa. The interstitium filled the intertubular spaces and was composed mainly of fine collagenous connective tissue which contained abundant Leydig (interstitial) cells and blood capillaries. The testis during winter appeared evacuated from the spermatozoa with no cystic arrangement of the germinal cells. The testis showed different degrees of vacuolation. The tubular lumen contained residual sperms. The vacuoles appeared in the Sertoli cells. Phagocytic cells were observed in close association of the basement membrane of Sertoli cells.