The aim of the present study was to investigate the effects of xenoestrogens, like nonylphenol (NP) on growth performance and gonads development of male Nile tilapia. Fish were randomly distributed into four groups in 16 fiberglass tanks with carrying capacity of 15 fish/tank and four replicates. Fish were exposed to different concentrations of NP. The contaminations of NP were 0, 25, 50 and 100 μgL^-1 administrated for 126 days. After exposure period, fish weight and survival were measured. Gonads and liver were dissected for calculating both Gonado- Somatic Index (GSI) and Hepato- Somatic Index (HSI) and processed for histological examination. At the end of the exposure period in all treated groups, the average survival rate was significantly lower than that of the control. The average body weights were ranged between 73.41 ± 1.37g - 78.14 ± 6.86g for the control and 50 µg NP L^-1, respectively with no statistical significant differences. Results showed slight changes in liver weight among treated group compared to the control. A significant (P<0.05) reduction in gonads weight and GSI occurred in exposed fish compared to the control. Testicular sections from the control group appeared fully mature where, lumens and ducts were loaded with spermatozoa. However, testicular sections from NP exposed fish showed germinal epithelium degeneration, which correlated with exposure level of NP and reflected on low weight of the gonads. The presence of oocytes within the testicular tissue was pronounced, especially in high dose exposed fish. Therefore, severity of testis-ova was mild in 25 µg NP L^-1, moderate to pronounced in 50 and 100 µg NP L^-1 exposed groups, respectively. From the obtained results, it could be concluded that the environmental pollutants with estrogenic activity such as nonylphenol can alter the development of gonads and disrupt reproduction of wild and farmed fish.