Background : Impetigo is mostly caused by either Staphylococcus aureus(S. aureus) or group A β-hemolytic Streptococcus(Streptococcus pyogenes). As the relative preponderance of each microorganism varies greatly, so reports have been contradictory. Recently, S. aureus has been reported as the principal causative microorganism of impetigo and shown variable degrees of antimicrobial resistance. Objective : The purpose of this study is to find out the main causative microorganism and the antibiotic susceptibility of causative organism in impetigo. Method : Bacterial cultures and antimicrobial susceptibility test were done in 55 patients with impetigo. Results : S. aureus was cultured from 49 patients of 55 patients(89.1%), and the remains were coagulase negative Staphylococcus, Streptococcus, Citrobacter braakii and Klebsiella. The resistant rates of S. aureus against antibiotics were as follows ; penicillin : 98.0%, gentamicin : 69.2%, tobramycin : 65.0%, tetracycline : 62.5%, erythromycin : 57.1%, piperacillin : 36.0%, clindamycin : 17.4%, cefazolin : 9.5%, ciprofloxacin : 8.1%, imipenem : 5.0%, oxacillin : 3.9%, trimethoprim-sulfamethoxazole : 3.7%, cefuroxime : 0%, nobobiocin : 0%, teicoplanin : 0%, and vancomycin : 0%, Methicillin-resistant S. aureus(MRSA) and oxacillin-resistant S. aureus(ORSA) were cultured in three of 20 patients(15%) and one of 26 patients(3.9%), respectively The resistant rates of MRSA or ORSA against other antibiotics were as follows ; cefazolin, ciprofloxacin, erythromycin, and penicillin : 100%, tobramycin : 67%, trimethoprim-sumfamethoxazole : 25%, and teicoplanin, vancomycin, and nobobiocin : 0%. Conclusion : S. aureus was the most prominent pathogen in impetigo in this study and sensitive to cefuroxime, nobobiocin, teicoplanin, vancomycin and oxacillin, but not to penicillin, gentamicin, tobramycin, tetracycline and erythromycin. The effective antibiotics in the treatment of MRSA or ORSA were vancomycin, nobobiocin, teicoplanin and trimethoprim-sulfamethoxazole.(Korean J Dermatol 2003;41(10) : 1278~1285)