Abstract: Group A streptococci is the most important causative agent of tonsillo-pharyngitis. Erythromycin is drug of choice in patients who are allergic to -lactams. The aim of this study was to determine the prevalence of streptococcus pyogenes resistant to erythromycin and other commonly prescribed antimicrobial agents. This prospective study conducted in Mazandaran province teaching hospitals. Patients with fever and tonsillo-pharyngitis were enrolled: Throat culture was obtained at the time of admission. Antimicrobial susceptibility test was done. All 85 isolates of streptococcus pyogenes were sensitive to penicillin, amoxicillin, cephalexin. and clindamycin however 3 cases had poor response to penicillin therapy. The resistance rate to erythromycin, tetracycline and ceftriaxone were 28, 46 and 3.5%, respectively.