BACKGROUND It has been reported that polysaccharides have potential novel anti-cancer properties. Previously, we confirmed that Dictyophora polysaccharides could significantly inhibit liver transplantation tumors in mice. However, the mechanism of Dictyophora polysaccharide action on human liver cancer is unclear. Here, we aimed to clarify the mechanism of Dictyophora polysaccharide action on human hepatocellular carcinoma cells, namely the effect on cell proliferation, the cell cycle, and apoptosis, and on the apoptosis-related genes and proteins in vitro. MATERIAL AND METHODS The HCC-LM3 cell line was incubated with 2.5 mg/mL Dictyophora polysaccharides for 24, 48, and 72 h. The cell growth inhibition rate was evaluated using Cell Counting Kit-8. Cell cycle and apoptosis were measured with flow cytometry. The expression of apoptosis-related genes and proteins was measured using real-time fluorescence quantitative polymerase chain reaction (RT-qPCR) and Western blotting, respectively. RESULTS The Dictyophora polysaccharides inhibited HCC-LM3 cell proliferation in a time- and dose-dependent manner and blocked the cell cycle in the G₂/M phase. In addition, Bax and caspase-3 expression were significantly increased after Dictyophora polysaccharides treatment. CONCLUSIONS To the best of our knowledge, this is the first published study on the mechanism of Dictyophora polysaccharide inhibition of HCC-LM3 cell proliferation.