Abstract: Five isozymes (EST, ME, AST, LDH and MDH) from six tissues (muscle, heart, liver, kidney, brain and spleen) of Trachinotus ovatus were preliminarily studied using vertical polyacrylamide gradient gel electrophoresis. The results showed that the tissue specificity of these isozymes is very obvious. The expression of enzyme gene loci and the activity of isozyme varied with different tissues. The number of EST isozyme bands was 3, which was encoded by 2 gene loci. Est-1 expressed in all 6 tissues, and Est-2 only existed in liver and kidney. The number of LDH isozyme bands was 3, which was encoded by 3 gene loci. Ldh-2 only expressed in kidney. Two divisions of MDH were found from T.ovatus. It was encoded by 2 loci, and the most specific MDH was in liver. The isozyme bands of MDH3 also existed in all 6 tissues. The number of ME isozyme band was 1, which was encoded by 1 loci. AST isozyme which was encoded by two loci was only found in liver and kidney.