The effect of Photoperiod manipulation on growth and some aspects of reproductive performance in Nile tilapia (Oreochromis niloticus) was studied at Animal Production Department, Faculty of Agriculture. The experimental work was conducted at Central Laboratory for Aquaculture Research Center, Ministry of Agriculture, Egypt . Ninety females and Ninety males Tilapia fish (50±5g) each was reared in aquaria of 150x50x50 cm and treated with three different photoperiods: 18 L: 6 D, 6 L: 18 D, and natural photoperiod 12 L: 12 D (L, Light; D, Dark). Each treatment consists of 30 males and 30 females which were divided into three replicates. In whole experimental period which lasted for 6 months, other environmental factors were maintained at constant level like, light intensity (500 Lux), water temperature (28°C), pH (9) and dissolved oxygen (6 mg/l). Under these conditions and treatments females and males were weighed and the ovary weight, egg weight, egg number, egg diameter, spawning periodicity and sperm count were recorded. The results showed an increase in male and female weights with increasing time and exposure to photoperiod. Also, ovary weight, egg weight, egg number, egg diameter have the same trend. Long photoperiodic exposure has positive effect on spawning periodicity of Nile Tilapia. The final weights of females and males after six months were significantly higher in L 18:6 D than other light treatments. Egg diameter, final egg number per female, and egg weight were increased significantly with increasing photoperiod. Also, the average final sperm count per male in different light schedules was significant. Long photoperiodic exposure has positive effect on (spawning periodicity) mean time interval until first spawn and mean ISI (inter-spawn-interval) in different light periods were enhanced in longer photoperiod than other treatments .The final average serum estradiol in female and final serum testosterone in males are in favor of longer photoperiods than short or natural photoperiod. It could be concluded that growth and reproduction performance in O. niloticus can be improved by exposing Nile Tilapia to 18 hours light: 6 hours dark and water temperature of 28°C and pH 9.