The bacterial flora of chronic maxillary sinusitis has been the subject of numerous investigation. Various techniques have been employed to obtain a representative specimen of maxillary sinusitis. Mixed infection and the presence of saprophytic bacteria have often reported. Author reviewed 76 patients of chronic maxillary sinusitis from October 1-76 to May 31-77 in National Medical Center and analysed bacterial strains and it's sensitivity to antibiotics. The material for bacteriological examination has been obtained by antral puncture with saline irrigation or swabbing of pus in sinus by using of sterile cotton stick during Caldwell-Luc's operation. The reuslts were obtained : 1. Among 100 sinuses, bacteria was isolated in 87 sinuses and other sinuses were sterile. 2. Among 87 isolated strains, 75 cases (86.20%) were single strain, 9 cases (10.34%) two strains and 3 cases (3.46%) three strains respectively. 3. Among isolated strains, H. influenza were 35 strains (40.23%), staphylococcus 19 strains (21.84%), normal throat flora 12 strains (13.79%) and pseudomonas 7 strains (8.04%) respectively. 4. Number of bacterial flora and mixed infection were fewer in sample obtained during Caldwell-Luc's operation than that of antral irrigation. 5. The percentage of sensitive strains were higher against leucomycin 100%, cloxacillin 100%, kanamycin 83.33%, ampicillin 73.68%, carbenicillin 73.68% and penicillin 70.45%, The percentage of resistant strains were higher against erythromycin in 75.92%, tetracycline 56.35%. 6. H. influenza strains were sensitive to gentamycin, doxycycline, leucomycin and resistant to erythromycin and cephalosporin. 7. Staphylococcus strains were sensitive to leucomycin, cloxacillin and resistant to erythromycin, chloramphenicol and penicillin. 8. Pseudomonas strains were resistant to streptomycin, tetracycline, gentamycin and doxycycline.