Abstract: The effect of oyster oligopeptide on regulation of immune function in cyclophosphamide (CTX)-induced immunosuppressive mice was evaluated. Different dosages of oyster oligopeptide (50、100、200 mg/kg) were given to the low, middle, and high group mice. The group injected with CTX was adopted as model group, with the group without treatment as the control group. The index of immune organs such as liver, spleen and so on, the transformation and propagation ratio of T lymphocyte, the activity of NK cell, the humoral immunity, macrophage phagocytosis, the level of cell cytokines and hemolysin were all assessed. The experiment results revealed that compared with the model immunosuppressed group, oyster oligopeptide could significantly enhance the proliferation of spleen lymphocyte, NK cell activity, expurgation index k, devouring index a, ability of devouring neutral red, the level of TNF-、IL-6 and hemolysin, and regulate the distribution of CD3+4T and CD3+8T spleen lymphocyte subsets. However, the influence of oyster oligopeptide on the immune organs was not significant. Hence, it was concluded that oyster oligopeptide can improve the cell immunity, humoral immunity and non-specific immune function of immunosuppressive mice induced by CTX, and it can regulate the immune function positively in mice.