Paranasal sinusitis, especially maxillary sinusitis, is a very common disease in the otorhinolaryngological field. There are numerous articles reported about the bacteriological studies on the maxillary sinusitis in adult, but rare in children. Thus the author examined 63 patients(84 sinuses) with signs and symptoms suggestive of maxillary sinusitis and abnormal maxillary sinus radiographs who had tonsillectomy and adenoidectomy from February 1985 to March 1987. Bacterial specimens were obtained by antral puncture. The following results were obtained. 1) The sex incidence was 44 males and 19 females, and age distribution was from 3 yrs to 14 yrs. 2) Organisms were isolated from 49 sinuses(58.3%) of 86 sinus culture and 37 sinuses(41.7%) were sterile. Among the 49 sinuses, 41 cases(90.5%) have single strain, 8 cases(9.5%) have mixed strains. 3) Radiographic findings were total haziness in 44 sinuses and mucosal thickening in 40 sinuses. Among the group of total haziness in 44 sinuses, bacteria was isolated in 30 sinuses(68.1%), and among the group of mucosal thickening in 40 sinuses, 19 sinuses(47.5%) were isolated. 4) Among 57 isolated strains(including mixed infection), the most frequently encountered organism were Staphylococcus aureus in 20 strains(35.1%), Staphylococcus epidermidis 9(15.8%), α-Hemolytic streptococcus 8(14.0%), Streptococcus pneumonia 3(5.3%), Non-enterococcal streptococcus group D3(5.3%), Enterococcus group D3(5.3%), Normal nasal flora 2(3.5%), Moraxella species 2(3.5%), Streptococcus sanguis 1(1.8%), Streptococcus pyogenes 1(1.8%) and Alkaligenes faecalis 1(1.8%) in order. 5) Staphylococcus strains were sensitive to Cephalothin, Cefotaxime, Methicillin, Chloramphenicol, Lincocin, Gentamycin and resistant to Ampicillin, Penicillin, Erythromycin. α-Hemolytic streptococcus were sensitive to Chloramphenicol, Ampicillin, Cefotaxime, Cephalothin and resistant to Penicillin, Methicillin, Tetracycline, Lincocin, Gentamycin.