Hizikia fusiformis, a brown alga that is widely consumed in Korea, Japan, and China, possesses a number of potentially beneficial compounds, including antioxidants and anticoagulants. However, the molecular mechanisms of H. fusiformis in hepatoma cells have not been elucidated. This study investigated the antiproliferative effect and mechanism of action of a glycoprotein from H. fusiformis (HFGP) in HepG2 human hepatoma cells. In an MTS assay, 25 ${mu}g/mL$ HFGP inhibited the proliferation of HepG2 cells by $52.36{pm}2.37%$. HFGP caused the dose-dependent growth inhibition of HepG2 cells by inducing apoptosis and a sub-G1 phase arrest. The antiproliferative activity of HFGP was confirmed based on the expression of several apoptosis-related proteins, which was assessed by Western blot analysis. The expressions of Fas, Fas-associated death domain protein, Bax, and Bad was significantly up-regulated in HFGP-treated cells, and HFGP induced the translocation of Bax to mitochondria and the release of cytochrome c into the cytosol. Therefore, HFGP might be useful in the treatment of liver cancer.