This study performed to examine the ability of pawpaw (Carica papaya) seeds to induce sterility in male and female of Nile tilapia (Oreochromis niloticus). Five groups were prepared; negative control group with mixed sex fish (G1) and positive control with monosex fish (G2) fed on basal diet, while G3, G4 and G5 were mixed sex fish fed on basal diet with addition of 60, 90, 120g of C. papaya seeds/kg diet, respectively. Ten fish with average weight of 30±1g were stocked at each of fifteen tanks (triplicates/treatment) with dimensions 135×50×60cm. Gonado-somatic index (GSI), egg diameter, fecundity and plasma sexual hormones level were determined and histological examination of gonads were performed. GSI, egg diameter and fecundity of treated females decreased significantly (P≤0.05) after treated and recovery months, while GSI of males was not significantly different (P≥0.05) among treatments. The levels of testosterone (T) and estradiol (E2) significantly (P≤0.05) decreased after treated and recovery months. All values decreased gradually with increasing the dose of C. papaya seeds. Histological sections showed several structural changes in testes and ovaries of the treated groups with different degree according to C. papaya seeds dose. Sections after recovery month showed that C. papaya seeds induced permanent sterility in the high dose while the low and medium doses may have reversible effect. The study concluded that, the seeds of C. papaya can be used with adjusted amount as a feed additive to control the problem of precocious maturity and breeding of O. niloticus in growing ponds instead of unfavorable and expensive hormone.