Abstract: Objective To investigate effects of Forsythoside (FS) on the proliferation and function of different tissue macrophages separated from mice. Methods Peritoneal, bone marrow and spleen macrophages were prepared by aseptic technique from 56 Kunming mice killed by cervical dislocation and in vitro cultured in media containing different concentration FS (40, 80, 160 mg.L-1) alone or respectively together with lipopolysaccharide (LPS). Cell proliferation was detected by MTT, TNF-α and NO level were assayed by ELISA and Griess method respectively. Phagocytic ability of peritoneal macrophages was analyzed by Wright-Giemsa staining method. Results Compared with LPS group, it were very significantly increased in absorbance values of peritoneal macrophage treated with FS and of bone marrow macrophages stimulated with FS+LPS, but decreased markedly in those of spleen and bone marrow macrophages treated with FS and of peritoneal and spleen macrophages with FS+LPS. In addition, FS was very significantly improved cell proliferation of spleen and bone marrow macrophages while significantly inhibited that of peritoneal macrophages from mice injected by cyclophosphamide (CY). TNF-α secretion levels of different tissue macrophages in FS group were significantly lower than those of the control and LPS group. FS significantly increased NO secretion level of LPS-stimulated peritoneal macrophages and reduced that of spleen macrophages and also there was a significant dose-dependence, while there was not markedly change in NO level of bone marrow macrophages. FS significantly inhibited NO secretion levels of spleen and bone marrow macrophages from CY-treated mice but did not affect peritoneal macrophages. FS could enhance the phagocytosis of LPS-stimulated peritoneal macrophages to chicken red blood cells. Conclusion FS had an impact on cell proliferation of different tissue macrophages, TNF-α and NO secretion, and phagocytic ability, which may be one of FS mechanism to regulate cellular immune function.