Hericium erinaceus is valuable in the diet and in medical treatment. It contains water-soluble polysaccharides that have been found to enhance immunity and which show anti-artificial pulmonary metastatic tumor effects. In this study, water and ethanol extracts of the mycelium and fruiting body of Hericium erinaceus were examined by the Ames test using Salmonella typhimurium TA98 to screen for antimutagenic effects against 5 mutagens: AFB1, B[a]P, Glu-P-1, NQNO, and Trp-P-1. We found that both extracts have the strongest antimutagenic activity against Trp-P-1, followed by Glu-P-1, B[a]P-1, AFB1, and finally NQNO. In addition, the antimutagenicity of the extracts was produced in a concentration-dependent manner. At a concentration of 200 ppm, both extracts showed the highest inhibitory action. However, the linear correlation indicated that concentration-activity relationship was not significant (p > 0.05). In addition, extracts showed less antimutagenicity after heat treatment (p < 0.05). This suggests that the antimutagenicity of the extracts is heat-labile. The ethanol extract from mycelium or fruiting body had better antimutagenic effects than did the water extract (p < 0.05). Also, the extract from the fruiting body had better antimutagenic effects than did that from the mycelium.