The chemical composition of diets is appointed as one responsible by different results of L-carnitine supplementation in fish. This study determined the effects of digestible dietary protein (DP; 250 and 290 g kg-1) and crude fat (CF; 100 and 150 g kg-1) at levels of DL-carnitine supplementation (DLC; 0 and 1.0 g kg-1) in plant based-diets on growth and whole-body composition of Nile tilapia Oreochromis niloticus fingerlings (1.55 ± 0.03 g). Fish were hand-fed for 74 days, three times per day until apparent satiation, in a completely randomized experimental design, 2×2×2 factorial scheme (n = 3). There was no effect (P > 0.05) of DP, CF, and DLC, or interactions, on growth performance. There was a significant interaction between DP×CF; DP×DLC and DLC×CF on feed efficiency. There was interaction (P < 0.05) between CF×DLC on feed intake (DFI). The DLC supplementation in 100 g kg-1 CF diets increased DFI 5.6% more than fish fed with the same fat level without DLC. Whole-body protein decreased significantly due to DLC supplementation in fish fed with 150 g kg-1 CF diets. The level of DLC supplementation in Nile tilapia diets is variable and should consider the dietary CF levels, but not DP.