Abstract: The effects of Phytolacca acinosa polysaccharides Ⅰ (PAP-Ⅰ), a polysaecharide extracted from Phytolacca acinosa Roxb: on splenic lymphocyte proliferation and cytokines production from splenic lymphocyte and macrophage were studied. Lipopolysaceharides (LPS) and PAP-Ⅰ were found to significantly augment splenic lymphocyte proliferation of normal BALB/c, nude BALB/e and NC mice in vitro, but concanavalin A (Con A) was shown to stimulate only normal BALB/c and nude BALB/c splenic lymphocyte proliferation. Also, PAP-Ⅰ significantly enhanced Con A or LPS-indueed lymphocyte proliferation and mixed lymphocyte reaction. Significant enhancement of colony stimulating factor (CSF) production was observed from splenic lymphocyte of normal BALB/c and nude BALB/c mice but not from NC mice when treated with PAP-Ⅰ for 5 d. PAP-Ⅰ was shown to significantly enhance interleukin-2 (IL-2) production from normal mice splenocyte and Con A stimulated normal mice splenocyte in a concentration-dependent fashion. Supernatant of PAP-treated macrophage (MΦ) were collected and CSF activity was tested. The results confirmed that PAP-Ⅰ can significantly stimulate MΦ to secret CSF activity on d 1. The supernatant also contained a cytokine which exhibited a synergistic action with recombinant murine granular—macrophage CSF (RMGMCSF) to stimulate mice bone marrow cell proliferation. PAP-Ⅰ, 5～50 mg · kg^-1, ip can enhanced splenic lymphocyte proliferation and IL-2 production. These findings indicate that PAP-I can augment immunologic function in vitro and in vivo.