Objective: To investigate the effect of docosahexaenoic acid (DHA) on proliferation and apoptosis of human hepatocellular carcinoma Bel-7402 cells and its mechanism. Methods: The cell proliferation characteristics and expressions of Bcl-2 and Bax proteins after exposure of Bel-7402 cells to different concentrations of DHA (0, 25, 50, 100 and 200 μmol/L) for different time periods (24, 48 and 72 h) were measured by MTT assay and Western blot analysis, respectively. Moreover, the apoptosis, Bim gene expression and caspase-3 activity in Bel-7402 cells exposed to the above concentration gradients of DHA for 48 h were determined by flow cytometry, real-time PCR and caspase-3 activity assay kit, respectively. Results: Different concentrations and time periods of DHA treatments showed that the proliferation of Bel-7402 cells was significantly inhibited in a concentration- and time-dependent manner (all P<0.05), and the Bax protein expression was increased while Bcl-2 protein expression was decreased in Bel-7402 cells in a concentration-dependent (all P<0.05) but time-independent manner (both P>0.05). After exposure to different concentrations of DHA for 48 h, the apoptosis, Bim gene expression and caspase-3 activity of Bel-7402 cells were all significantly increased in a concentration dependent manner (all P<0.05). Conclusion: DHA can inhibit the proliferation and induce the apoptosis of Bel-7402 cells, and the mechanism may possibly be associated with the activation of the mitochondrial apoptotic pathway.