Abstract: The study was conducted to investigate the effects of replacement of fish meal protein by crystalline amino acids on digestive enzymes and metabolism enzymes in tongue sole larvae. Five isoproteic and isolipidic diets were formulated to replace 0%, 25%, 50%, 75%, 100% fish meal (0% CAA, 25% CAA, 50% CAA, 75% CAA and 100% CAA) respectively. At the replacement level of 25%, another diet was formulated with amino acids coated with tripal-mitin (C-25% CAA). Each micro diet was randomly fed to triplicate groups of fish, and each group had 150 fish. The results showed that the activities of trypsin significantly decreased with increasing dietary crystalline amino acids, but there were no significant differences between C-25% CAA and 0% CAA (P0.05). The ratio of Trypsin(I) to Trypsin(P) significantly decreased with increasing dietary crystalline amino acids, and 0% CAA was significantly higher than 75% CAA and 100% CAA. The activities of amylase significantly increased with increasing dietary crystalline amino acids. The activities of leucine-amino peptidase and alkaline-phosphatase in intestine and purified brush border membrane of intestine significantly decreased with increasing dietary crystalline amino acids, but no significant differences were observed between C-25% CAA and 0% CAA (P0.05). Glutamic-pyruvic transaminase and Glutamic-oxalacetic trans-aminease significantly increased with increasing dietary crystalline amino acids. In conclusion, crystalline amino acids in the micro diet significantly influenced the digestive and metabolic enzymes of tongue sole larvae. In the replacement level of 25%, Comparing with 25% CAA group crystalline amino acids coated with tripalmitin (C-25% CAA) could promote the development of digestion system in tongue sole larvae.