Chronic suppurative otitis media is one of most common disease in the otolaryngologic field. There are many reports in this study but they are some difference each other. The author has performed the bacteriological study in 100 cases(male 51, female 49) of chronic suppurative otitis media who visited the department of otolaryngology, Guro hospital during a period of June 1984 through August 1985 and the following results are obtained. 1) In age distribution, 3rd decade is most prevalent(43.0%) and next are 2nd decade(25.0%). 2) 0-5 years is most common duration(24.0%) and next is 20-24 years(20.0%). 3) Among 100 cases, 78 cases(78.0%) are unilateral, in details, right ear are 40 cases and left ears are 38 cases, and 22 cases are bilateral. 4) The positive cultures are 89 cases(89.0%) but 11 cases are no growth. Among 89 cases, single infection is 65 cases(73.0%) and mixed infection is 24 cases(27.0%). 5) The most frequently isolated bacteria is staphylococcus aureus(23 strains, 20.4%) and next are proteus mirabilis(22 strains, 19.5%) and pseudomonas aeruginosa(22 strains, 19.5%). 6) Cholesteatomatous otits media is 34 cases(34.0%). Among them, most common causative organisms are staphylococcus aureus(19.4%), proteus mirabilis(19.4%) and pseudomonas aeruginosa(19.4%). In non-cholesteatoma cases, staphylococcus aureus is most common(21.6%) and next are propteus mirabilis(20.3%) and pseudomonas aeruginosa(20.3%). 7) Staphylococcus aures is sensitive to cefotaxim(100%), cephalothin(91.3%), methicillin(85.7%) and resistant to penicillin(91.9%), ampicillin(81.0%), tetracyclin(66.7%). 8) Proteus mirabilis is sensitive to cefotaxim(100%), amikacin(100%), cephalothin(94.1%) and resistant to teracycline(100%), chloramphenicol(55.6%), kanamycin(55.0%). 9) Pseudomonas aeruginosa is sensitive to amikacin(100%), tobramycin(72.7%), cefotaxim(61.6%) and resistant to tetracyclin(100%), ampicillin(100%), cephalothin(95.7%), kanamycin(95.5%), chloramphenicol(95.2%).