Objective: To investigate the roles of phosphatidylinositol 3-kinase regulatory subunit alpha （PIK3R1）gene in the development of hepatocellular carcinoma （HCC）. Methods: Surgical specimens of liver cancer and corresponding pericancerous liver tissue were collected from 20 patients with hepatocellular carcinoma. Expression of p85α, encoded by PIK3R1, in HCC tissue specimens was detected by Western blotting and immunohistochemistry. HCC HepG2 cells were transfected with PIK3R1 siRNA or PIK3R1-cDNA. The expression of PIK3R1 in transfected HepG2 cells or control cells were detected by real-time PCR. Cell proliferation was evaluated by MTT, colony formation assays and flow cytometry respectively. The expression of PI3K/AKT pathway-related proteins were detected by Western blotting. Results: The expression of p85α in liver tissue was higher than that in pericancerous tissues （1.27±0.58 vs 0.99±0.47, t=-3.25, P<0.05）. The expression of PIK3R1 was decreased by 0.19±0.03 fold in PIK3R1siRNA-transfected HepG2 cells （t=46.77, P<0.05）, and increased by 32.36±3.33 fold in PIK3R1 cDNA-transfected cells （t=-16.31, P<0.05）. MTT result showed that PIK3R1 siRNA inhibited growth of HepG2 cells （0.611±0.072 vs 0.807±0.059, t=3.65, P<0.05）, while PIK3R1 cDNA increased the cell growth （0.937±0.060 vs 0.693±0.065, t=-4.78, P<0.05）. PIK3R1 siRNA transfected cells presented lower colony-forming efficiency than control group （3.8%±0.84% vs 15.0%±2.3%, t=7.92, P<0.05）, while PIK3R1 cDNA transfected cells had higher colonyforming efficiency than control group （23.6%±3.4% vs 12.0%±1.5%, t=-5.40, P<0.05）. PIK3R1 siRNA reduced the ratio of S phase cells （13.9%±0.015% vs 32.9%±0.07%, t=45.97, P<0.01）, while PIK3R1 cDNA increased S phase cells （56.33%±0.024% vs 31.94%±0.042%, t=-8.73, P<0.01）. PIK3R1 increased the level of p-AKT and decreased p53 level. Conclusion: p85α is highly expressed in HCC, and PIK3R1 gene may promote proliferation of HepG2 cells by activating PI3K/AKT pathway.