The study investigated the effects of heat shock protein 70(HSP70)antisense oligonucleotide (ASODN)on the proliferation and apoptosis of a human hepatocellular carcinoma cell line(SMMC-7721 cells)in vitro.HSPT0 oligonucleotide was transfected into SMMC-7721 cells by the mediation of SofastTM transfection reagent.Inhibition rate of SMMC-7721 cells was determined by using MTT method.Apoptosis rate and cell cycle distribution were measured by flow cytometry.Immunocytochemistry staining was used to observe the expression of HSP70,Bcl-2 and Bax.The results showed that HSP70 ASODN at various concentrations could significantly inhibit the growth of SMMC-7721cells,and the inhibition effect peaked 48 h after transfection with 400-nmol/L HSP70 ASODN.Cytometric analysis showed the apoptotic rate was increased in a dose-and time-dependent manner in the HSP70 ASODN-treated cells.The percentage of cells in the G2/M and S phases was significantly decreased and that in the G0/G1 phase increased as the HSP70 ASODN concentration was elevated and the exposure time prolonged.Immunocytochemistry showed that treatment of SMMC-7721 cells with HSP70 ASODN resulted in decreased expressions of HSP70 and Bcl-2 proteins,and an increased expression of Bax protein.It was concluded that the HSP70 ASODN can inhibit the growth of the SMMC-7721 cells and increase cell apoptosis by down-regulating the expression of HSP70.HSP70ASODN holds promise for the treatment of hepatocellular carcinoma.