The effects of DL -carnitine and L -carnitine with different supplement doses (200mg·kg -1DL carnitine , 400mg·kg -1 DL -carnitine and 200mg·kg -1 L -carnitine) on the growth and composition of body of hybrid tilapia ( Oreochromis nilotica ♀× Oreochromis aurea ♂) were studied with a mean body weight of 38. 65 ±0.21g per fish over 34 days. The study showed that the two isomers of carnitine neither improve the growth rate nor alter the composition of whole fish and muscle significantly , but it was observed that the relative weight of viscus was changed and the liver fat decreased significantly ( P < 0. 05) . No clear difference of supplement effects between DL -carnitine and L -carnitine with same supplement dose (200mg·kg -1) was found under the experiment conditions .