AIM: To explore the effect of turtle blood extract on murine immune system. METHODS: We compared the ratio of CD4(+) helper T cells and CD8(+) T cells, NK cell activity, lymphocyte proliferation stimulated by mitogen and capability of cytokine secretion of cyclosphophamide-treated mice with or without treatment of turtle blood extract. RESULTS: Turtle blood extract-treated mice displayed increased CD4(+) helper T cell population, stronger cytotoxicity of NK cells and enhanced of ConA-induced lymphocyte proliferation. In addition, the capacity of IFN-gamma secretion was dramatically up-regulated in turtle blood extract-treated mice group. CONCLUSION: Turtle blood extract can upregulate the immune function of cyclosphophamide-treated mouse.