An experiment was conducted to evaluate the effects of dietary nucleotide on growth and reproduction performance of Nile tilapia ( Oreochromis niloticus ) in brackish water (8 ppt). Four experimental diets were formulated using different levels of exogenous nucleotide as follows: 0 (control), 0.05, 0.1, and 0.15%. Each diet was randomly allocated to triplicate groups of fish with initial average weight of 52 g. Fish were fed 2-3 % of their body weights, two times a day (8:00 and 16:00) for 45 days. At the end of the rearing period growth, hematological (hematocrite, hemoglobin, red blood cell, white blood cell, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC)) and biochemical (total protein, cholesterol, triglyceride, glucose, albumin, Aspartate Transaminase and Alanin Transaminase) parameters were recorded. The control group and fish fed the highest nucleotide level (0.15 % NT) were subjected to cold stress. Blood samples were taken at 0 (before stress), 3 and 6 hours after stress for serum cortisol and glucose measurments. The results showed significant improvement in final weight, weight gain, daily growth rate and specific growth rate in fish fed on nucleotide as a supplement in a dose response manner. Feed conversion ratio decreased and the lowest FCR (1.19) was observed in group of fish fed on diet containing 0.15 % NT. There was an increasing trend in the level of some hematological parameters but there were no significant changes among groups (P 0.05). Results from cold shock stress showed an elevation in the cortisol and glucose levels after stress exposure in both groups, although fish fed on the NT showed significantly lower levels of cortisol and glucose in comparison to the control group. At the end of rearing period, appropriate broodstock were selected from each treatment and stocked in breeding tanks at the sex ratio of 3?:1?. Fish were fed on experimental diets during 90 days as reproduction period. Results showed that some reproduction indices such as working and relative-working fecundities, hatching, yolk sac absorption and larval survivel rates were improved significantly in fish fed on the NT; while egg composition and diameter, initial and final wights of the larvae were not affected. As a consequence, it could be advisable to use dietary nucleotide as a growth and reproductive enhancer in Nile tilapia in brackish water cultivation practice. Key words: Nucleotide, Nile tilapia, Oreochromis niloticus , growth, reproduction, brackish water.