Abstract: The objective of this work was to select probiotic bacterial strains for juvenile sea cucumber Apostichopus japonicus.Three strains of potential probiotics isolated from the intestines of A.japonicus were identified by 16S rDNA sequence genotyping as Bacillus GSC-1, Bacillus GSC-2 and Enterococcus GSC-3.The safety of these potential probiotics was evaluated by immersing juvenile A.japonicus in sea water with GSC-1,GSC-2,GSC-3 or Vibrio splendidus at 10⁰,10³,10⁵ or 10⁷ CFU/mL respectively for 7 days. Results showed that GSC-1 and GSC-3 treatments were safe under the designed concentrations based on the mortality rates. However,GSC-2 caused significantly higher mortality at 10⁷ CFU/mL than the blank control(P<0.05).A 20-day feeding trial was conducted to investigate the effects of GSC-1 and GSC-3 on the growth performance and innate immune response of juvenile A.japonicus.Feeds were algae(Sargassum thunbergii)powder supplemented with GSC-1 or GSC-3 at 0(control)and 10⁹ CFU/g respectively.The specific growth rate and survival rate were significantly increased in treatment supplemented with GSC-1.Comparatively,survival rate and discoloration rate were remarkably improved in treatment of GSC-3(P<0.05).Moreover,GSC-1 increased total bacteria counts and decreased Vibrio spp.counts significantly(P<0.05).Phenoloxidase and lysozyme activities in body tissue of the juvenile A.japonicus were significantly higher in the group treated with GSC-1 or GSC-3 than the control(P<0.05)while acid phosphatase and superoxide dismutase activities were remarkably higher than control in GSC-1 group only(P<0.05).Both GSC-1 and GSC-3 showed positive effects on disease resistance of juvenile A.japonicus,especially GSC-3 significantly improved disease resistance to V.splendidus exposure(P<0.05).In conclusion,both Bacillus GSC-1 and Enterococcus GSC-3 show probiotic effects,therefore they can be used as probiotics in the farming of juvenile sea cucumber A.japonicus.