A bacteriologic study was made on 55 cases of immediate post-operative infection of chronic otitis media patient who visited the Department of Otolaryngology, Chosun University Hospital from July, 1992 to August, 1995. The present study has focused on the comparison of bacteriologic results between intra-operative and post-operative discharge when a post-operative infection was developed. The following conclusions were reached. 1) The most frequently isolated bacteria from discharge at operation were Staphylococcus aureus(13 strains, 23.2%) and followed by Pseudomonas aeruginosa(12 strains, 21.4%), Proteus mirabilis(6 strains, 8.9%). After operation, bacteria isolated from discharge were S. aureus(41 stains, 62.1%), P. aeruginosa(6 stains, 9.0%) and P. mirabilis(4 stains, 6.1%). 2) After the opertion, S. aureus which was cultured from discharge was 41 stains. Among them, 10 stains(24.4%) were related with isolated bacteria during the operation and the otehrs (31 stains, 75.6%) were not. 3) After the operation, P. aeruginosa which was cultured from discharge was 6 strains. Among them, 5 strains(83.3%) were related to isolated bacteria from operation and the other(1 strain, 16.7%) was not. 4) After the operation, bacteria isolated from discharge were 66 stains. Among them, bacteria which were related to operation were 18 stains(27.3%), including S. aureus(10 stains), P. aeruginosa(5 stains), and P. mirabilis(2 stains). It was suggested that these infections were probably caused by the contamination of postoperative dressing, or overgrowing of normal flora.