The present study is continuation to the first step in a comprehensive program for producing "supermale_s" (YY) of Oreochromis niloticus in Egypt to produce all male tilapia for increasing fish production and prevent unwanted reproduction in ponds. Sexually undifferentiated fry after yolk sac absorption period were feminized using 17-0 ethynylestradiol incorporated into the feed. Fry were reared in hapas suspended In an earthen pond and fed for three time durations, 3, 4 and 5 weeks on three different dosages of the feminizing stimulating agent (FSA) 50, 100 and 150 mg/kg/ feed. Growth of fry was affected by the dosages used. Average weight of fry that were fed on higher doses of 17-13 ethynylestradiol supplemented feed was significantly higher than those fed on lesser amounts for the same period. The effect of 17­p ethynylestradiol as a (FSA) was highly detectable among a niloticus fry (1 generation) that were fed on 150 mg/kg (FSA) -treated feed for 5 weeks. Progeny test was adopted to estimate the mean percentage of phenotypic females MPF that reached 92.0 2.3% when fry were fed for 5 weeks on 150 mg/kg (FSA) treated -feed. MPF decreased with decreasing the quantity of (FSA) in the supplementary feed. The length of feeding period when interacted with the (FSA) dose in the supplementary feed had an appreciable effect on sex reverse among progenies of 0.  nilolias. After rearing of the sex reversed fry to sexual maturity and crossing normal males (xy) to the undifferentiated pseudo- and normal females (t­xy and roc), twenty four converted pseudofemales with female phenotype and xy male genotype could be differentiated by progeny testing of their offspring (2"^d generation) that consisted male percentage varying from 69 to 79% males exceeding the normal ratio. Hypothetically, one third of these males should be super males of the "rr genotype and two thirds should be normal males. Further research by crossing these males after sexual maturation to normal females and testing their progeny will prove' or disprove this hypothesis.