Objectives: The purpose of this study was to compare the oral antimicrobial effects of seven different mouthwashes available in Korea. Methods: To examine the antimicrobial effects of the seven mouthwashes, their minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were determined using broth microdilution methods. Streptococcus mutans ATCC 25175, Lactobacillus acidophilus ATCC 4355, Candida albicans KCTC 7270, and Porphyromonas gingivalis ATCC 33277 were used in this experiment. S. mutans and P. gingivalis were examined using a scanning electron microscope (SEM), after treatment with the mouthwashes containing cetylpyridinium chloride (CPC). Results: Mouthwashes containing CPC had lower MIC and MBC values against the four microorganisms. Their bactericidal effects were concentration-dependent. S. mutans and C. albicans were highly sensitive to the concentration of CPC in the mouthwashes. According to the SEM observation, the treatment of bacteria with mouthwashes containing CPC, changed the cell surface texture of S. mutans and P. gingivalis. Conclusions: Mouthwashes containing CPC showed relatively lower MIC and MBC values under the same conditions against the four microorganisms used in this study.