The effect of dietary L-carnitine and lipid on growth performance and body composition of Nile tilapia, Oreochromis niloticus was evaluated in this study. A 4×2 factorial design was utilized to test the efficiency of L-carnitine at a rate of 0, 300, 600 and 900 mg/kg diet at each of two lipid levels (10 and 15%). Therefore, eight isonitrogenous (30%) and isocaloric (3000 kcal ME /kg diet) were formulated and fed twice daily to two replicate groups of Nile tilapia. Fish of all groups were initially weighed and then every 2 weeks for 8 weeks. It was found that body weight (BW) was significantly increased in groups fed dietary L-carnitine 900 mg/kg at dietary lipid levels 10 and 15% compared with control groups. Specific growth rate (SGR) was significantly increased in groups fed dietary L-carnitine 600, 900 mg/kg at both dietary levels. Weight gain (WG) was significantly increased in groups fed L-carnitine 300, 600 and 900 mg/kg diet at dietary lipid level 10 and 15% compared with control groups. Feed conversion ratio (FCR) was significantly decreased in all groups supplemented with L-carnitine. Tissue protein percent was significantly increased in groups supplemented with L-carnitine at dietary lipid 15%. The diet contained 15% lipids caused significantly increase in SGR and WG compared with dietary lipid 10%. Results of this study revealed that using L-carnitine in concentration of 600 and 900 mg/kg diet at 15% dietary lipid could improve growth rate and increase tissue protein taking in consideration the economic cost of L-carnitine supplementation to fish diets.