Objective To investigate the growth inhibition of human osteosareoma cell line(MG-63) intervened by Hydralazine and 5'-aza-2'-deoxycytidine (5-Aza-CdR),and the effect on the mRNA expression of gene WW domain-containing oxidoreductase (WWOX).Methods Certain volume of 5 × 104/ml of human osteosarcoma cell line MG-63 in logarithmic growth phase were added into 96-well plate.There were Hydralazine group (drug concentration,0.1,1.0,10 μmol/L),5-Aza-CdR group (drug concentration,5,10,20 μmol/L),Hydralazine combined with 5-Aza-CdR group (drug concentration,0.1 μmo/L + 5 μmol/L,1.0 μmol/L + 10 μmol/L,10 μmol/L + 20 μmol/L) and control group (culture medium).Methyl thiazol tetrazolium(MTT) colorimetric methods were used to test the growth inhibition of MG-63 cells intervened by different concentrations of Hydralazine and 5'-aza -2'-deoxycytidine (5-Aza-CdR).Flow cytometry AnnexinV-FITC/PI methods were used to assay the effects of Hydralazine and 5-Aza-CdR inducing apoptosis in osteosarcoma cells in vitro.Real-time polymerase chain reaction (Real-Time PCR)methods were used to detect amplification of WWOX mRNA induced by Hydralazine combined with 5-Aza-CdR or alone.Western-blotting methods were used to examine the expression of WWOX in MG-63 cells.Results Hydralazine and 5-Aza-CdR effectively inhibited the growth of MG-63 cells in a concentration and time-dependent manner.Combined effect was more obvious.Further more the expression levels of WWOX mRNA and protein were increased significantly in combined groups as compared with other groups.Conclusion Hydralazine and 5-Aza-CdR could effectively inhibit the proliferation of MG-63 cells and induce apoptosis which is concurrent with the promotion of the expression of WWOX.The mechanism may be that Hydralazine/5-Aza-CdR effectively cause the demethylated of WWOX gene CpG-rich promoter regions,leading to the high expression of WWOX and inhibit the growth of MG-63 cells.The use of hydralazine in the treatment of osteosarcoma is worthy of further investigation.