Abstract: The present study was conducted to estimate the optimum requirement of dietary available phosphorus for adult GIFT strain of Nile tilapia Oreochromis niloticus reared in freshwater.Six semi-purified diets were formulated to contain graded levels(0.15%,control diet,0.40%,0.66%,0.91%,1.17% and 1.43%t)of available phosphorus(KH₂PO₄ was the source of phosphorus).Each diet was fed to triplicate groups of 20 fish with initial average weight(184.46±8.13)g for 9 weeks.The results showed that fish fed the two diets with available phosphorus levels of 0.66% and 0.91% had significantly higher weight gain rate(WGR)and specific growth rate(SGR)than those fed the other diets(P<0.05),and the feed efficiency(FE)was significantly higher than that of control diet(P<0.05).The whole body viscerosomatic index(VSI),hepatosomatic index(HIS)and condition factor(CF)decreased significantly with the increases of the dietary available phosphorus levels(P<0.05),while the survival rate(SR)of fish had no significant differences among various dietary treatments(P＞0.05).Crude protein,ash,and phosphorus concentration in whole body increased significantly with the increases of the dietary available phosphorus levels,as well as vertebrae and scale ash and phosphorus concentration(P<0.05).Crude lipid concentration in whole body decreased significantly with the increases of the dietary available phosphorus levels(P>0.05).Quadratic curve analysis based on SGR indicated that the minimum dietary requirement of available phosphorus for maintaining maximal growth of tilapia was 0.85%.