This study was conducted to determine the nutritional value of different protein levels of practical diets for Nile tilapia (Oreochromis niloticus) fingerlings (mean initial body weight 14.78g). The experimental diets were designed to contain four different dietary protein (CP) levels, 20(D1), 25(D2), 30(D3) and 35% (D4). The results showed that there were significant differences (P<0.05) among the final average body weight of fish (at the end of the 12 weeks feeding period). The average final body weights of fish fed the experimental diets were 99.62, 100.74, 107.32 and 116.91g for fish fed D1, D2, D3 and D4, respectively. Total feed intake was significantly (P<0.05) increased with increase in dietary protein level. The values of feed intake (FI) were 143.61, 149.22, 152.31 and 161.82g for tilapia fed D1, D2, D3 and D4, respectively. Also, specific growth rate (SGR) showed a similar trend with significant differences (P<0.05) among treatments with values being 2.29, 2.27, 2.37 and 2.45%/d for fish fed the four experimental diets in respective order. Feed conversion ratio (FCR) almost significantly (P<0.05) decreased with decreasing dietary protein level in the diet, being 1.69, 1.74, 1.64 and 1.59 for fish fed D1, D2, D3 and D4, respectively. Protein efficiency ratio (PER) decreased significantly for fish fed D3 (2.01) and D4(1.80) compared with the other two diets D1(2.60) and D2(2.27). Also, protein productive value (PPV) decreased with increasing dietary protein level with significant differences (P<0.05). The viscera-somatic index (VSI) and hepatosomatic index (HSI) showed significant differences (P<0.05) among treatments. Data of proximate analysis of whole fish bodies showed that dietary protein level had no significance different (P>0.05) in dry matter, protein and ash contents of whole fish body. Whereas, fish fed D3 and D4 had significantly (P<0.05) higher ether extract (EE) contents in their bodies compared with fish fed D1 and D2. The results of the present study indicated that, the optimal protein requirements of monosex Nile tilapia fingerlings reared in fiberglass tanks ranged between 30 and 35% without any natural foods.