The aim of this study was to investigate the susceptibility of mutans streptococci (S. mutans and S. sobrinus) and Streptococcus anginosus, for seven antibiotics, penicillin G, amoxicillin, ciprofloxacin, cefuroxime, erythromycin, bacitracin, and vancomycin. The minimum inhibitory concentration (MIC) of seven antibiotics against 3 species (type strains) of mutans streptococci and S. anginosus, 10 strains (wild type) of S. mutans, 7 strains (wild type) of S. sobrinus, and 11 strains (wild type) of S. anginosus, were measured by broth dilution method. All of the type strains of mutans streptococci and S. anginosus had the same susceptibility for penicillin G, amoxicillin, cefuroxime and bacitracin. Type strain of S. anginosus was sensitive in ciprofloxacin, but those of mutans streptococci were not. All of the clinical isolates of mutans streptococci and S. anginosus had the same susceptibility for the seven antibiotics. Our data reveal that mutans streptococci and S. anginosus have similar antibiotic-resistant character. In addition. these results may offer the basic data to verify the antibiotic-resistant mechanism of mutans streptococci and S. anginosus.