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Objective: Multiple myeloma is a kind of malignant plasma cell disease that originated from B lymphocyte and secrete great amount of monoclonal immunoglobulin. It is still one of the refractory diseases at present. Numerous studies show that there is an intensive relationship between the disequilibrium of histone acetylation and the occurance of multiple myeloma. Here we investigated the effect of triptolide(TPL) on the proliferation, apoptosis, histone H3 and H4 acetylation and expression of histone deacetylase 8 (HDAC8) in vitro, to explore its anti-myeloma mechanism.Methods: The effect of triptolide on the growth of RPMI8226 was studied by 3-(4,5-Dimethyl-2-thiazolyl) -2,5-diphenyl-2H-tetrazolium(MTT) assay. Apoptosis was detected by Hoechst 33258 staining. The protein expressions of acetyl-histone H3 and H4 were determined by West blot, and the expression of HDAC8 was assessed by RT-PCR, West blot and confocal microscopy.Results: Triptolide inhibited the proliferation of RPMI8226 and induced apoptosis in a time- and dose-dependent manner. The 36h IC50 value was (105.370±0.189)nmol/L. Triptolide increased the acetylation of histone H3 and H4 greatly. Furthermore, triptolide significantly down-regulated the mRNA and protein expression of HDAC8.Conclusion: Triptolide can inhibit proliferation and induce apoptosis of RPMI8226 significantly. Triptolide reduces the expression of HDAC8 in order to increase the histone H3 and H4 acetylation, which is possibly the anti-myeloma mechanism of triptolide.