This study was carried out to investigate the effect of temperature on some reproductive performance and estrogen levels in female Nile tilapia (Oreochromis niloticus). An obvious significance increase in 23 Assiut Vet. Med. J. Vol. 51 No. 104 January 2005 gonado-somatic index (GSI) was shown by increasing temperature (16+1, 19+1, 25 1, 28 = 1 and 32-1) respectively. The present results provided empirical evidence that temperature increased egg production significantly by increasing temperature in fish treated groups (16+1, 19+1, 25 + 1, 28 = 1 and 32+1°c) respectively. Concerning oocyte maturation, the present results revealed a significant increase in the percentage of oocyte maturity by increasing temperature in treated groups at (16+1, 19+1, 25 £ 1, 28 = 1 and 32+1°c) respectively. Moreover, results in this study showed significant increase in estrogen level in the groups under elevated temperature (25+1, 28+1 and 32+1 °c).On the other hand, no spawning was observed in groups of fish treated with water temperature at 16+1 and 19+1°c. Water temperature not only affects spawning frequency but also affects different reproductive performance in O. nilotica where an inverse relationship between water temperature and incubation period and inter spawning interval was recorded. The differences between fish treated with water temperature 25+1, 28+] and 32 +1 °c respectively were statistically significant for incubation period, rearing period and interspawning interval. These results indicated that temperature consider the key factor for promoting the reproductive and physiological performance in female Nile tilapia (O. niloticus).