In consideration of the differences between Neomysis awatschensis and Neomysis japonica in the growth,reproduction,susceptibility and other aspects,the susceptibility of two Neomysis to Vibrio alginolyticus was studied,which could help to explore to the root of the phenomenon in immunology.Two staining methods of Giemsa and wright’s were used in this experiment of the haemocytes of the adult N.awatschensis, and haemocytes of the mysis were classified base on the large/small size,the presence/absence of cytoplasmic granules,the number of granules,and nucleus to cytoplasm(N/C)ratio and the proportion of various haemocytes were also carried out.The results of these studies showed:three types of haemocytes were identified in N.awatschensis hyaline cells,semigranular cells,granular cells,ascending in the size and declining in the N/C ratio,successively.To further check the statistics of the rate of three types haemocytes,the observations indicated that the highest rate of granular cells was about(48.38%?0.05%),the lowest of hyaline cells about(16.40%?0.01%),the moderate rate of semigranular cells about(35.22%?0.04%).By contrasting the dyeing time and dyeing effect of the two staining methods,Wright’s staining was more appropriate for the mysis haemocytes.When exposured in aquaculture water containing various concentration of V.alginolyticus,N.awatschensis began to die at 72 h while N.japonica at 48 h,and had a higher death rate than that of N.japonica in all the concentrations.Compared with N.japonica,N.awatschensis was less susceptible to V.alginolyticus, and the reason of such difference could be associated with the higher ratio of granular cells(including semigranular and granular cells)in N.awatschensis.