Assessment of optimum salinity level (10‰, 15‰, 20‰, 25‰ and 30‰) for growth performance, food conversion, body composition and survival rate of Nile tilapia, Oreochromis niloticus (mean body weight 4.5±0.5 g) were investigated. Fingerlings were randomly distributed into the glass tanks (60 x 30 x 45 cm each). Ten fish per tank were stocked with two replications. Fish were fed with commercial floating pellet (35% protein) with 3% of total biomass day-1 for 50 days. Results showed that the growth increment reared on 10‰ - 20‰ salinity were significantly highest in term of weight gain, WG % of initial weight, daily weight gain, specific growth rate, condition factor and survival rate than those reared on 25‰ and 30‰. Feed conversion ratio was found similar in all levels which is not significantly different (P> 0.05). Whole body composition i.e. protein (53.16% – 53.26%), moisture (71.16% – 71.26%), lipids (2.49% – 2.52%), ash (4.16% – 4.18%) contents of fish whole body were not significantly (P>0.05) different at varying salinity levels. Mean values of water quality were found acceptable for tilapia i.e. temperature 28.42±0.08°C, dissolved oxygen 7.48±0.06 mg/L, pH 7.64±0.04 and ammonia 0.022±0.004 mg/L. Relationship between log body weight and log total length of the the fish shows that Nile tilapia fingerlings reared from 10‰ - 20‰ was significantly (P <0.05) higher than 25% and 30% salinity levels. Present study suggests that Nile tilapia can be reared up to 20% salinity to get good growth and higher survival rate.