Abstract: A 20 days feeding experiment was conducted to study the effects of probiotics on immune enzyme activity(alkaline phosphatase AKP,a cidic phosphatase ACP,superoxide dismutase SOD,catalase CAT and lysozyme UL)and anti-WSSV ability of Litopenaeus vannamei. Diets were supplemented with Photobacterium damsela (live,≥10¹¹ CFU/g or inactivated,1 g/kg)or Bacillus firmus (live,≥10¹¹ CFU/g or inactivated,1 g/kg).Controls were fed non-supplemented diet.In this experiment,feeding the bacteria species(inactivated P.damsela; live Bacillus firmus)significantly increased serum ACP,AKP,SOD and CAT compared with controls(P<0.05),at the same time,their cumulative morality were(49%?15%)and(53%?12%)respectively,which were significantly increased compared with controls(P<0.05).The present results suggested that the diets supplemented with B. firmus (live) or P. damsela (inactivated)could improve immune enzyme activity and anti-WSSV ability of shrimp,and the probiotics with the function of preventing disease could be used as one of effective ways of biological prevention and control to WSSV.