OBJECTIVE To study the effect of basil polysaccharide on the expression of histone methyltransferase G9a, demethylase JMJD1A and histone H3K9me2 methylation level in hepatoma cells MHCC97H and MHCC97L under hypoxic conditions, in order to explore the regulatory effect of basil polysaccharide on the epigenetics of hepatoma cells. METHODS Cobalt chloride(CoCl2) was used to simulate hypoxic, MHCC97H and MHCC97L hepatoma cells hypoxia model was established in vitro,and then intervened with different concantration of basil polysaccharide intervened 24 h. The expression of HIF-1α, G9a and JMJD1A mRNA in hepatoma cells were detected by real time fluorescent quantitative PCR. The expression of HIF-lα, G9a, JMJD1A protein and histone H3K9me2 methylation level was detected by Western-blot method. RESULTS Basil polysaccharide down-regulated the expression of HIF-lα, G9a, JMJD1A mRNA and protein and histone H3K9me2 methylation level in MHCC97H cells under hypoxic condition,and down-regulated the expression of HIF-lα mRNA and protein and histone H3K9me2 methylation level in MHCC97L cells under hypoxic condition(P <0. 05). CONCLUSION Basil polysaccharide can regulate histone H3K9me2 methylation levels in hepatoma cells MHCC97H and MHCC97L which have different metastatic potential under hypoxic conditions. On hepatoma cell MHCC97H, the regulation of histone H3K9me2 methylation is associated with histone methyltransferase G9a and demethylase JMJDlA. In hepatoma cell MHCC97L, the regulation of histone H3K9me2 methylation was probably through other pathways.