Abstract: AIMTo evaluate the effect of polysaccharide from Spirulina platensis (PSP) on hematopoietic cell proliferation, apoptosis and Bcl-2 expression in mice bearing tumor treated with chemotherapy. METHODSThe model of chemotherapy for transplant solid tumor in mice was established. The hematopoietic cell proliferation, apoptosis, Bcl-2 expression and related cytokines were assayed by the technique of culture of hematopoietic progenitor cell, fluoromicroscope and light microscope, immunohistochemical method, and double antibody sandwich ELISA. RESULTS PSP significantly ameliorated CFU-GM proliferation inhibition and hematopietic cells apoptosis induced by CTX. Moreover, PSP evidently increased the content of IL-1, IL-3, GM-CSF and TNF-α in serum and Bcl-2 expression of hematopoietic cells. CONCLUSIONPSP indirectly upregulated Bcl-2 expression of hematopoietic cells by promoting endogenous cytokines secretion which may be one of the mechanisms, by which PSP enhanced hematopoietic cell proliferation and inhibited its apoptosis in mice bearing tumor treated with chemotherapy.