Abstract: The research evaluated the effects of photosynthetic bacterium PS2 on the growth performance, digestive enzymes and serum nonspecific immune enzymesof cultured sea bass (Lates calarifer). Four levels of Rhodopseudomonas capsulate liquid product at concentration of 8108 cfumL-1 were supplemented to a basal diet at 0.0 % (control group), 0.5 % (group 1), 1.0 % (group 2) and 1.5 %, respectively. Diets were fed to the sea bass with initial body weight of (10.950.25) g for 50 days. The results showed that there was no significant difference in the weight gain, specific growth rate, survival rate and feed conversion ratio among all experimental groups (P0.05). The liver protease, intestinal and stomach amylase of group 2 were significantly higher than those of the control group(P0.05). The intestinal protease of group 3 was significantly lower than that of group 2 (P0.05), but there was no significant difference between the experimental group and the control group(P0.05). The pyloric caeca digestive enzymes of group 3 were significantly higher than those of the other groups (P0.05). There was no significant difference in serum AKP, POD and SOD among the groups (P0.05). Theresults indicated that photosynthetic bacterium PS2 had no significant effects on the growth performance and nonspecific immune ability of the sea bass, but it could promote the activity of digestive enzymes of pyloric caeca in group 3 and improve significantly that of theliver protease, intestinal amylase and stomach amylase in group 2 (P0.05).