Abstract: Objective The Xeroderma Pigmentosum D (XPD) gene plays an important role in the path to DNA repair. It has been reported that cells obtained high tumor susceptibility when mutation happened in XPD gene. The purpose of this study is to investigate the influence of XPD gene in the growth and proliferation of hepatoma carcinoma cells (HCC). Methods pEGFP-N2 and pEGFP-N2-XPD were transfected into SMMC-7721 cell lines by Lipofectamine2000 method. The expression of green fluorescent protein (GFP) was observed through fluorescence microscope. Cell cycle of the plasmid-transfected SMMC-7721 cells was analyzed by Flow cytometry (FCM). The expressions of wild-type XPD, c-myc, cdc25A and cdK2 were detected by RT-PCR and Western blot. Cell proliferation was measured by MTT assay. Results The recombinant plasmid pEGFP-N2-XPD was successfully transfected into SMMC-7721 cells and green fluorescence in cells was observed by fluorescent microscopy. Around 30% transfection efficiency was obtained in this experiment. In addition, we have found that wild type XPD blocked the hepatoma cells from S stage to G1 stage The expression of XPD in SMMC-7721-pEGFP-N2-XPD cells was significantly higher than those in control group of SMMC-7721 and SMMC-7721-pEGFP-N2 cells (P<0.05). The expressions of c-myc, cdc25A and cdK2 in SMMC-7721-pEGF-N2-XPD cells were significantly lower than those in control cells (all P<0.05). Furthermore, SMMC-7721-pEGFP-N2-XPD has reduced proliferation ability than empty plasmid-transfected cells (P<0.05). Conclusion Wild-type XPD downregulated the expression of c-myc, cdc25A, and cdK2. Our results suggested that XPD inhibit the proliferation of SMMC-7721 cells probably due to the blockage at S period DNA damage checkpoint in hepatocellular carcinoma cell cycle.