The current study was aimed to investigate the development of testis during pre-hatching periods to diverse the components of the testis in duck embryo from embryonic day 5 to 19 consequently; fifteen males' of mallard ducks embryos have been used. The results showed that development of testis has divided into two periods: the first one was the period of undifferentiated gonad (genital ridge) while the second period was the development into a testis which showed various stages. The undifferentiated stage has revealed of development a small protruded thickening of germinal epithelium and primordial germ cells on the ventromedial surface of the mesonephros and dorsal mesentery.The development periods has showed three stages: development of rete cords, sexual cords,primary somniferous tubules and Sertoli progenitor cells at the 8-10th day embryos. During 14th day old embryo was revealed of development immature somniferous tubule, tunica albuginea and testicular capsule. While the period of 19th day embryo showed that development of interstitial cells and thin septa from tunica albuginea, .in addition to marked division of spermatogonia cells. Size of left testis was larger than the right one also the epithelial layer of left gonad is thicker than that covering the right gonad.