Abstract: The inhibitions of strain H06091(Vibrio harveyi) of coelomic fluid(containing coelomocyte),suspension of coelomocyte(without coelomocyte),and suspension of coelomocyte and homogenate of endothelial tissue were detected in healthy and challenged sea cucumber Apostichopus japonicus by colony counting methods.The inhibition to V.harveyi,Staphylococcus albus and Edwardsiella tarda and basic characteristics were studied in water-solubility component from homogenate of endothelial tissue of the sea cucumber by ethanol precipitation and centrifuging method.The results showed that the endothelial homogenate had significant inhibition of V.harveyi,but the coelomic fluid containing coelomocytes,suspension of coelomocyte(without coelomocyte)and suspension of coelomocytes had no inhibition.The inhibition of the endothelial homogenate to bacteria was found to be reduced in the infected sea cucumber.The water-solubility component showed inhibition of V.harveyi,S.albus and E.tarda.The water-solubility component was found positive ninhydrin reaction and had protein content of 17.48% with five bands,molecular weight of about 55 300,46 100,34 700,19 500 and 14 500 by SDS-PAGE.The water-solubility component from the endothelial homogenate of the sea cucumber was showed to contain antimicrobial peptides.