Abstract: In order to classify the haemocytes of adult Neomysis japonica, light and electron microscopical studies were carried out. According to the presence or the absence of cytoplasmic granules, nucleus/cytoplasm(N/C)ratio, the number of granules with different sizes and electron-density of their cytoplasmic granules, three types of haemocytes were recognized in adult Neomysis japonica: type 1 hyaline cells(no cytoplasmic granule), type 2 semigranular cells(a few cytoplasm granule), type 3 granular cells(abundant granules in cytoplasm). The proportion of the three types were analyzed depending on Wright’s smears, and the result indicated that the proportion of haemocytes(47.53%±0.02) was the largest, while that of hyalinocytes(21.24%±0.02) the smallest. The size was increased from type 1 to type 3, however, the N/C rate was decreased. The activites of acid Phosphatase(ACP), alkaline phosphatase(AKP), lysozyme(LYZ), and phenoloxidase(PO) were analyzed by biological and chemistry methods in total body of Neomysis japonica on 0 d，10 d， 20 d， 30 d after being hatched，respectively. The activities of ACP， AKP, LYZ, PO were decreasing with the growth of individuals．The activity of LYZ was 305.20 U/mg Prot on average, the highest in the three enzymes； the second is ACP, at 0.236 5 U/mg Prot； The activities of PO and ACP were almost the same at 0.129 5 U/mg Prot in adult N. japonica．In conclusion, hyaline cells were mainly haemocytes type in adult N. japonica．In addition, lysozyme played a siginificant role in immune process of N. japonica．The activities of ACP, AKP, LYZ, PO were decreasing gradually with the individual development．