The purpose of this study was to isolate and identify the bacteria in chronic maxillary sinusitis (CMS) lesions from 3 patients and to determine the antimicrobial susceptibility of them against 10 antibiotics. One of them was odontogenic origin and the others were non-odontogenic origin. Pus samples were collected by needle aspiration from the lesions and examined by culture method. Bacterial culture was performed in three culture systems (anaerobic, CO2, and aerobic incubator). Identification of the bacteria was performed by 16S rRNA gene (16S rDNA) nucleotide sequencing method. To test the sensitivity of the bacteria isolated from the maxillary sinusitis lesions against seven antibiotics, penicillin G, amoxicillin, tetracycline, ciprofloxacin, cefuroxime, erythromycin, clindamycin, and vancomycin, minimum inhibitory concentration (MIC) was performed using broth dilution assay. Our data showed that enterobacteria such as Enterobacter aerogenes (30%), Klebsiella pneumoniae (25%), and Serratia marcescens (15%) were predominately isolated from the lesion of non-odontogenic CMS of senile patient (70 year old). Streptococcus spp. (40.3%), Actinomyces spp. (27.4%), P. nigrescens, M. micros, and P. anaerobius strains were isolated in the lesion of odontogenic CMS. In the lesion of non-odontogenic CMS, Streptococcus spp. (68.4%), Rothia spp. (13.2%), and Actinomyces sp. (10.5%) were isolated. The susceptibility pattern of 10 antibiotics was determined according to the host of the bacteria strains ratter than the kinds of bacterial species. Even though the number of CMS was limited as three, these results indicate that antibiotic susceptibility test must be accompanied with treatment of CMS. The combined treatment of two or more antibiotics is better than single antibiotic treatment in the presence of multidrug-resistant bacteria in the CMS lesions.