A set of 2400 of Nile tilapia fry (Oreochromis niloticus) with average initial weight of 0.02g, about six days of age was collected from a private fish farm in Kafr El-Sheikh Governorate. The fry were randomly divided into 24 similar groups and stocked in the experimental aquaria (100 fry in each). Experimental groups (24) were assigned to the 17a-MT hormonal treatments at concentrations of 0, 20, 40, 80, 160 and 320 mg/kg feed for 21 and 56 days (2 groups/treatment). Two basal diets were formulated to contain 45 and 35% crude protein (CP). All experimental fish groups were fed on the basal diet contained 45% CP in a powder form during the first 7 weeks, while the fish were offered a diet containing 35% CP in a 1mm pelleted form during the other 18 weeks of the experimental period. The optimum level of 17a-MT hormone used in tilapia sex reversal is 40 mg/kg feed and increasing 17a-MT level over 40 mg/kg feed resulted in decreasing percentage of male produced. Both of hormonal treatment and treatment periods did not significantly affected the growth performances of experimental tilapia fish.  There were no significant differences among the treated fish groups, while a significant increase was found in the survival rate in the short treatment period (21 days). Hormonal treatment resulted in abnormal structure of the tilapia fish gonads including semeniferous tubules degeneration and atrophy of the interstatial tissue.