Microbicides are used to eliminate pathogenic bacteria, but they can also eliminate beneficial and normal bacteria. This study provides antimicrobial information of mandelic acid (MA) prior to its widespread use. The MA susceptibilities of Lactobacillus sp. and pathogens were determined by dilution method based on NCCLS protocol. The concentration of MA at 5.0 mg/mL inhibited 90% of the Lactobacillus sp., whereas a 1.25 mg/mL concentration inhibited the following pathogenic bacteria strains: Listeria monocytogenes KCTC3710, Yersinia enterocolitica ATCC23715, and Shigella sonnei ATCC9290. The minimal inhibitory concentration (MIC) for Escherichia coli O157:H7, Salmonella enteritidis KCTC12400, Salmonella gallinarum ATCC9148, Salmonella typhimurium ATCC29631, and Staphylococcus aureus KCCM40881 was at 2.5 mg/mL. These pathogens were also inhibited by addition of 1.0 M NaCl in 2 mg/mL MA solution (pH 5.0), while lactobacilli were not affected. These results indicate that MA can prevent disease and food poisoning when applied as a disinfectant in food industry, hospitals, and public places.