Probiotics are live microbial food supplements that are considered to be beneficial for humans and animals. Many researchers have showed that probiotic bacteria can be effective to decrease cancer risk. In this study, Antimutagenic activities of four probiotic Bifidobacterium and Lactobacillus spp. against three potent mutagen acrylic amide, sodium azide and 2-nitrofluorene were examined by Ames test using Salmonella typhimurium TA100. Results showed Bifidobacterium and Lactobacillus spp. can inhibit mutagen agents unit 40%, That is very good antimutagenic activity. Bifidobacterium bifidum PTCC 1644 displayed the highest antimutagenic activity than other bacteria (inhibition 52.22% acrylic amide, 50.80% sodium azide and 48.66%, 2-nitrofluorene). Antimutagenic activity was increased significantly when there were liver microsome extract (S ).