Chronic faucial tonsillitis has long been one of the most common diseases in the otolaryngologic field, and the tonsillectomy occupies the greater part of our operations performed at our department. This is a study of pathogens of tonsillitis and their sensitivities to antibiotics in 50 cases who received tonsillectomy at the Dept. of E.N.T., Han-Yang Medical Center from January to September 1979. The results were as following : 1. On surface swab, pathogens were cultured in 28 cases (56%) and α-hemolytic Streptococci 13 cases (26%), Staphylococcus aureus 12 cases (24%), Pseudomonas aeruginosa 2 cases (4%), Diplococcus pneumoniae 1 cases (2%) in order. Non-pathogens were cultured in 5 cases (10%) and Enterococci 2 cases (4%), Neisseria Catarrhalis 2 cases (4%), Spirocheta fusiform 1 cases (2%) in order. 2. On deep tissues, Pathogens were cultured in 38 cases (76%) and Staphylococcus aureus 25 cases (50%), α-hemolytic streptococcus 10 cases (20%), Pseudomonas aeruginosae 2 cases (4%), β-hemolytic streptococcus 1 cases (2%) in order. Non-pathogens were cultured 5 cases (10%) and Staphylococcus epidermidis 3 cases (6%), Ehterococcus 2 cases (4%) in order. 3. In 18 cases (36%), same pathogens were cultured on surface and deep tissues at times, and 11 cases of differential pathogens. And in 17 cases (34%), surface of tonsil were no cultured flora in spite of cultured 12 cases of pathogens in deep tissues, and total differential pathogens were cultured in 32 cases (68%). 4. In sensitivity test for common pathogens (Staphylococcus aureus 37 cases), Amiktam, Geopen, Cloxacillin, Panimycin, Minocin, Streptomycin, Gentamycin, and Cafamezine were noted to 100% sensitivity, and Penicillin and Ampicillin were noted to 80% resistance. Other pathogens were also resistance to penicillin and ampicillin.