The author have observed the mucous membrane and the bony walls of the maxillary sinus histopathologically with their clinical findings in chronic maxillary sinusitis. Thirty random cases (18 patients) were investigated among the patients who received Caldwell-Luc's operation, during the period from July, 1978 through June, 1979 in Seoul Adventist Hospital. The mucous membranes were obtained from the maxillary sinuses and bony pieces were also obtained from the anterior and medial walls of the maxillary sinuses, and were examined microscopically after H & E stains. The obtained results were as follows, 1) In the review of the changes of mucous membrane in 30 cases, the pathology revealed 50% of hypertrophic type, 13.3% of atrophic type, 20% of glandular type, 6.7% of follicular type and 10% of papillary type. 2) In the study of the bony changes in 30 cases the anterior wall revealed 60% of osteoclastic type 20% of osteoblastic type and 20% of normal. There were no different bony changes between the anterior and medial bony wall, histopathologically, except 1 case. 3) No specific relationships were found between the pathological findings of the mucous membrane and the bony changes in the sinuses. 4) It seems to be in no apparent relation between the pathological types of the mucous membrane and pneumatization of sinuses. 5) It seems to be in no relation between the pathological types of the mucous membrane of the sinus and pus accumulation in the sinus, but pus accumulation seems to influence on the degree of bony changes. 6) The duration of illness seems not to be influence on the pathological changes of mucous membrane of sinus but it seems to influence on the bony changes, especially on osteoclastic type. 7) The clinical prognosis was generally not affected by the pathological types of the mucous membrane of the sinuses.