Abstract: Disease problems have seriously threatened the development of Crassostrea hongkongensis aquaculture. Thus, finding suitable biomarkers for C. hongkongensis health assessment is important for preventing C. hongkongensis diseases. We investigated the effects of salinity stress, ammonia stress, immune stimulation and air exposure stress on the immune indexes of C. hongkongensis. The results show that the CAT activity increased significantly under both low-salt (Salinity 3) and high-salinity (Salinity 30) stress (P<0.05). High-salt stress also increased SOD and NOS activities significantly (P<0.05). The stress of high concentration of ammonia nitrogen (60 mg∙L^–1) caused a significant decrease in the CAT activity (P<0.05), while the activities of ACP and SOD increased significantly under both high and low concentration of ammonia nitrogen (6 mg∙L^–1) stress (P<0.05). Both Vibrio harveyi and lipopolysaccharide stimulation inhibited the CAT activity significantly (P<0.05). In addition, the CAT activity during air-exposure stress at 4 and 25 ℃ showed a significant decreasing trend (P<0.05). Therefore, CAT is more sensitive to environmental changes than other immunological indicators, which may be a health-related evaluation index of C. hongkongensis.