Carnitine is a key factor on metabolism of long-chain fatty acid in mitochondria of animals. It is also a limited nutrient in plant feedstuff. A 2×3 factorial designed study was conducted to evaluate the interaction of dietary lipid and carnitine levels on growth and body chemical compositions of giant grouper (Epinephelus lanceolatus) fed the plant-based diet. The fish meal protein was replaced by soy protein concentrate at 50% in diet. Two basal diets containing 12% and 18% lipid were each supplemented with L-carnitine at 0%, 0.03%, and 0.05%. Total of 6 experimental diets were fed to triplicate groups of juvenile grouper (initial weight: 11.09±0.14 g) in a recirculation system for 8 weeks. Weight gain, protein efficiency ratio, intraperitoneal fat content, and whole-body lipid content were significantly (p<0.05) affected by dietary lipid levels. These parameters were higher in fish fed the high lipid-diets than those in fish fed the low lipid-diets. However, the parameters were not influenced by the dietary carnitine supplementation. Carnitine concentrations in muscle but not in liver significantly increased by the increment of dietary carnitine levels. Regardless of dietary carnitine levels, muscle sum of n-6 fatty acids, linoleic acid (C18:2 n-6) and linolenic acid (C18:3 n-3) levels were higher but saturated fatty acids and C20-C22 fatty acids levels were lower in fish fed the high lipid diets. Results indicate that lipid but not carnitine in plant-based diet can improve growth and raise the tissue lipid content, C18:2 n-6 and C18:3 n-3 levels.