Our previous study showed that the supernatant of coelomic fluid from sea cucumber (Apostichopus japonicus) exhibited strong antibacterial activity to Micrococcus lysodeikticus, but had no obvious effects on the growth of Vibrio splendidus, V. harveyi, Pseudoalteromonas nigrifacien and Streptococcus dysgadysgalactiae. In order to study the variation of immune-related enzyme activities in A. japonicus coelomic fluid after different bacterial challenge, five bacteria (bacterial information was listed in Tab 1) described above were injected into A. japonicus, respectively, and then the activities of acid phosphatase (ACP) and alkaline phosphatase (AKP), superoxide dismutase (SOD), lysozyme (LYZ) and phenoloxidase (PO) were determined using p-nitrophenyl phosphate (pNPP) method, nitro blue tetrazolium chloride (NBT) method, M. lysodeikticus powder method and dopachrome formation method, respectively. The experiments of enzymatic activities determination were performed in quadruplication, and the data were expressed as means ± standard deviations (SD). Statistical analysis was carried out using the software SPSS 11.5. Differences in enzymatic activities between bacteria-challenged group and the control group were analyzed by one-way ANOVA. The level of significance was defined as P < 0.05. As shown in Fig.1-Fig.5, the challenge of V. splendidus induced significant increase of acid phosphatase and alkaline phosphatase activities, but great decrease of superoxide dismutase, lysozyme and phenoloxidase activities; challenge with V. harveyi caused significant increase of acid phosphatase, superoxide dismutase, lysozyme and phenoloxidase activities and irregular variation of alkaline phosphatase activity; after challenge with P. nigrifacien, acid phosphatase, lysozyme and phenoloxidase activities increased significantly, superoxide dismutase activity increased firstly, and then decreased, and alkaline phosphatase activity exhibited irregular variation; after challenge with M. lysodeikticus, acid phosphatase and phenoloxidase activities increased, superoxide dismutase and lysozyme activities increased firstly, and then decreased, however, lysozyme activity returned to control level at 72 h post challenge, and alkaline phosphatase activity also exhibited irregular variation; the challenge of S. dysgadysgalactiae resulted in an inhibition on alkaline phosphatase activity at 4 h, but notable promotion on the activities of other determined enzymes. The results suggested that phenoloxidase was one of the most sensitive and efficient immune factors in A. japonicus innate immune system; no regular differences in the induction of A. japonicus immune factors were observed between Gram-positive bacteria and Gram-negative bacteria; between M. lysodeikticus and other four determined bacteria, the most significant difference was observed in the induction of lysozyme, and lysozyme might be the principle immune factor involved in the extermination of M. lysodeikticus; the variation of immune factors induced by V. splendidus differed greatly from those induced by other four bacteria, and the five immune factors selected in this study had potentials in the application for early warning of vibrio diseases; S. dysgadysgalactiae had potential in the application for immunostimulants in A. japonicus.