The injibitory effect of Bacillus licheniformis AJ isolated from genitourinary normal flora as a new probiotics on the growth of diarrheal pathogens was studied. This B. licheniformis AJ inhibited the growth of E.coli O-157. Salmonella typhi and Shigella sonnei as well as the infectivity of rotavirus. However, it did not inhibit the growth of Helicobacter pyloriand human intestinal bacteria although it inhibited the harmful enzyme activity of human intestinal bacteria. B. licheniformis AJ seems to excret heat-lable growth-inhibitory protein, bacteriocin, into the media. These results suggest that B. lichenoformis AJ could be used as a new type of probiotics.