Abstract： Objective To evaluate effects of trichostain A (TSA) on cell proliferation, cell cycles, apoptosis and invasiveness of multiple myeloma cell line U266; as well as active changes of methylation regulating proteins including DNA methyl-transferase(DNMTs), methyl-binding domain (MBD) proteins: MBD2 and MeCP2 after treated with TSA. Methods U266 cells were treated with different concentrations of TSA for 12, 24, 48 and 60 h. The proliferation activity of U266 cells was detected by MTT and the IC50 of 24 h was calculated. After U266 cells were treated with IC50, cell cycles were check out by dying with PI. mRNA of matrix metalloproteinase-2(MMP-2), bc1-2, bcl-xl and methylation regulating proteins (DNMTs, MBD2 and MeCP2) were detected by real-time PCR. FCM and Western blotting were used to measure expressions of MMP-2 and MBD2. Results MTT results revealed TSA inhibited proliferation of U266 cells in a dose-and time-dependent manner and the IC50 of 24 h was 0.07 μmol/L FCM analysis showed that TSA could arrest the cell cycle in G0/G1 and the proliferation index (PI) in U266 cells [(49.90 0.39)%]were significantly different after exposed to TSA (0.7 μmnol/L for 24h compared with that in the control cells[(55.78 0.49)%](P <0.01). After treated by TSA, the 2-△△Ct of MMP-2, bcl-2 and bcl-xl were 0.71 0.06, 5.04 0.92 and 2.95 0.35, respectively. There were great changes on mRNA of DNMT, MBD2 and MeCP2. TSA could reverse the transcription of DNMT, MBD2 and MeCP2. Conclusion TSA can arrest the U266 cell cycle in GVG, to prevent its proliferation and promote apoptosis, which maybe greatly connect with the changes of the methylation regulating proteins.