The physicochemical characteristics and biological activities, including antioxidant activity, antimutagenicity, and cytotoxicity of hot-water extract of fruiting body of Hericium erinaceus, were investigated in this study. Hot-water extract of fruiting body of Hericium erinaceus contained carbohydrate (7.86%), protein (10.91%), and ${eta}$-glucan (3.62%). Water solubility of hot-water extract was 42.58%. Antioxidant activities of the extract were evaluated by ABTS assay and FRAP assay. The $IC_{50}$ value was 312.21 ${mu}g/mL$ in ABTS assay. Antimutagenic activity of the extract was evaluated by Ames test. Antimutagenicity of hot-water extract (5 mg/mL) on Salmonella Typhimurium TA100 mutagenated by sodium azide (0.15 ${mu}g/mg$) was 69.2%. Cytotoxicity of hot-water extract was also evaluated by MTT and SRB assay. The cytotoxicity was highest (83.95%) on Hep3B treated with 2,000 ${mu}g/mL$ of hot-water extract in SRB assay. Therefore, it is suggested that hot-water extract of fruiting body of Hericium erinaceus has high antioxidant activity, antimutagenicity, and cytotoxicity.