Antimutagenic effects of methanol extracts of various soybean pastes against aflatoxin B1 were examined using Salmonella typhimurium TA98 and TA100. Antimutagenic activities of boiled soybeans, Japanese Miso, traditional Korean soybean pastes, soybean pastes fermented by wild type strains, and soybean pastes fermented by mutants, transformants, and cell fusants were 53.6 to 54.6%, 73 to 79.7%, 78.3 to 95.7%, 85 to 97.1%, 71.9 to 78.3%, 65.5 to 77.7%, and 73.4 to 79.0%, respectively. Soybean pastes fermented by wild type strains showed higher activities than those fermented by mutant, transformant, and cell fusant strains.