Abstract: Objective To explore whether aspirin could sensitize arsenic trioxide on human hepatocelluar carcinoma cell line and understanding the combination mechanisms underlying co-treatment. Methods Cell viability was detected by MTT assay, cell apoptosis rate and reactive oxygen species (ROS) level were measured by flow cytometry, and Western blot assay was used to estimated the protein expression of heme oxygenase-1 (HO-1) in total protein and NF-E2-related factor 2 (Nrf2) in nuclear protein. Results 10 μmol/L arsenic trioxide can decreased the cell viability, while cell apoptosis rate, ROS level, HO-1 and Nrf2 protein expression was increased ( P<0.05). When compared with arsenic trioxide alone, co-treatment of arsenic trioxide with aspirin in different concentration (0, 0.1, 1.0, 2.5, 5.0 mmol/L) exhibited dual effects in intracellular ROS level, HO-1 and Nrf2 expression. Specifically, with the increasing of aspirin concentrations, the level of ROS induced by arsenic trioxide showed a rising trend after the first reduction, whereas, HO-1 and Nrf2 protein expression were decreased at first and then increased. Conclusion Low concentration, less than 2.5 mmol/L, of aspirin may reduce the ROS accumulation through activating of Nrf2-HO-1 pathway, therefore decreasing the apoptotic cell death induced by arsenic trioxide. On the contrary, 5 mmol/L aspirin could increase the sensitivity of HepG2 to arsenic trioxide through enhancing the arsenic trioxide-induced apoptosis by ROS accumulation resulting in inhibiting the Nrf2-HO-1 pathway.