OBJECTIVE To establish a convenient and efficient model for investigating the expression of CYP3A4 and drug metabolism in vitro. METHODS 1alpha,25-dihydroxyvitamin D3 was utilized as an inducer to enhance CYP3A4 expression in HepG2 cells. 0.1, 0.25, 0.35 micromol/L 1alpha,25-dihydroxyvitamin D3 were added to the cell culture media, and cells were harvested after 24, 48, 72 and 96 hours. Cell proliferation was determined with MTT assay. CYP3A4 mRNA level was analyzed with RT-PCR and expressions of CYP3A4 protein were measured by Western blot. RESULTS 1alpha,25-dihydroxyvitamin D3 in 3 concentrations, namely 0.10, 0.25 and 0.35 micromol/L, did not show obvious toxicity to HepG2 cells. At 24 h of the cultivation, the expression of CYP3A4 mRNA was not increased significantly, but CYP3A4 mRNA expression significantly increased by 120%, 134%, 200% at 48 h, by 174%, 254%, 420% at 72 h, and by 258%, 450%, 370% at 96 h, respectively under the three concentrations. Similar results were observed in the induction of CYP3A4 protein expression. At 48, 72 and 96 hours after treatment with 0.25 micromol/L and 0.35 micromol/L 1alpha,25-dihydroxyvitamin D3, CYP3A4 protein increased in various folds in the controls (1.2 and 2.2 after 48 h, 3.4 and 6.5 after 72 h, 6.1 and 7.2 after 96 h), while 0.10 micromol/L 1alpha,25-dihydroxyvitamin D3 only induced protein expression at 72 h and 96 h (1.8 and 4.1 folds, respectively). CONCLUSIONS 1alpha,25-dihydroxyvitamin D3 could induce the expression of CYP3A4 mRNA as well as CYP3A4 protein in HepG2, which provides a convenient and efficient in vitro system for investigation of CYP3A4 and drug interaction.