Abstract: AimTo study the effect of catechin, the active component of Spatholobus suberectus Dunn, on bone marrow cell cycle and the expression of IL-6 and GM-CSF mRNA in spleen cells of normal and marrow-depressed mice in order to clarify the mechanism of hematopoietic-supportive effect of catechin. MethodsFlow cytometry was adopted to investigate the influence of catechin on bone marrow cell cycle in mice and the expression of IL-6 and GM-CSF mRNA induced by catechin in spleen cells was detected by RT-PCR technique simultaneously. ResultsThe cell proportion of normal and marrow-depressed mice in G₀/G₁ phase was reduced significantly, while that in S+G₂/M phase increased significantly. Being induced by catechin, IL-6 mRNA and GM-CSF mRNA in spleen cells were markedly up-regulated. ConclusionCatechin (2 g·L^-1, intraperitoneally injected to mice daily immediately after irradiation for 7 consecutive days) was shown to promote the expression of IL-6 mRNA and GM-CSF mRNA in spleen cells of mice, through which it can accelerate bone marrow cells of normal mice into cell cycle and help those of marrow-depressed mice to get out of “G₁-phase-block”, enter into cell cycle and radically accelerate the proliferation and differentiation of hematopoietic stem cell/hematopoietic progenitor cell (HSC/HPC).