The author interested in the pathological changes of the bony walls of the maxillary sinus in case of the chronic paranasal sinusitis, one of the most prevailing and annoying ailments in our country. Thirty one the random cases (20 patients) were investigated among the patients who received Caldwell-Luc's operation during the period of a year from April, 1969 through March, 1970 in our university hospital. The bony pieces were obtained from the anterior (facial) and the medial walls (the lateral wall of the inferior nasal meatus) of the maxillary sinuses, and were examined microscopically under conventional H & E stain. The author also observed any relationship between the bony changes of the maxillary sinuses and the severity of the sinusitis or post-operative prognosis, etc. The results were obtained as follows : 1) In the review of the bony changes in 31 cases, the anterior walls revealed 77.4% of the osteoclastic type, 6.5% of the osteoblastic type and 16.1% of normal. The medial bony walls showed 71.0% of the osteoclastic type, 16.1% of the osteoblastic type, and 12.9% of normal. 2) There were no different bony changes between the anterior and medial bony walls except 5 cases (16.1%). 3) No specific relationships were found between the bony changes and the pathological findings of the mucous membrane of the sinus. 4) It seems no relationship between the bony changes and pneumatization of sinus but the osteoclastic change of bony walls were found more frequently in the cases of pus accumulation in the sinus cavity. 5) The duration of illness seems to influence on the bony changes. 6) The prognosis was generally not affected by the bony change, except a few cases which showed severe bony change.