Objective To investigate the effect of silymarin (SM) on the expression of hypoxia-inducible factor-1 alpha (HIF⁃1α) and multidrug resistance 1 (MDR1) in HepG⁃2 cells under hypoxia. Methods After treatment of HepG⁃2 cells with different concentrations of SM (0, 10, 20, 40 mg/L) and concentration gradient chemotherapeutic drugs (doxorubicin, sorafenib, cisplatin), MTT assay was used to detect the effect of different concentrations of SM on the sensitivity of HepG⁃2 cells to chemotherapeutic drugs. Under hypoxic conditions, HepG⁃2 cells were treated with SM at 0, 10, 20, and 40 mg/L for 8 h, RTPCR was used to detect the effects of different concentrations of SM on the expression levels of HIF⁃1α and MDR1 mRNA, and Western Blot was used to detect the effects of different concentrations of SM on the protein expression levels of HIF⁃1α and Pglycoprotein (P⁃Gp) in HepG⁃2 cells. Results With the increase of SM concentration, the sensitivity of HepG⁃2 cells to the chemotherapy drugs doxorubicin, sorafenib and cisplatin gradually increased. Compared with the control group, there was no significant difference in HIF⁃1α mRNA expression in the 10, 20, and 40 mg/L SM treatment groups (P>0.05), while the MDR1 mRNA expression decreased in a concentration-dependent manner (P<0.05). Additionally, the HIF⁃1α and P⁃Gp protein expression levels of the 10, 20, and 40 mg/L SM treatment groups decreased in a concentration-dependent manner compared with the control group (P<0.05). Conclusion SM might reduce the expression of MDR1 by inhibiting the expression of HIF⁃1α in HepG⁃2 cells at the post-transcriptional level, thereby reducing the drug resistance of hepatocellular carcinoma cells.