I have observed histopathologically the mucous membrane of maxillary sinus in 63 cases that received Caldwell-Luc's operation during the period from Jan., 1972 to Mar., 1979 in Han Gang Sung Sim Hospital. The results are as follows : 1) The pathological classification revealed edematous type(33 case, 52.4%) fibrous type(17 cases, 26.9%) and infiltrative type(13 cases, 20.7%) in 63 cases. 2) The most frequent state in glands are moderate hyperplasia(48.5%) in edematous type, normal or atrophic(47.0%) in fibrous type and moderate hyperplasia(61.5%) in infiltrative type. 3) The most frequent state on blood vesels are all moderate change in edematous(63.6%), fibrous(52.9%) and infiltrative type(61.5%). 4) The most frequent state in cell infiltration are minimal infiltration(63.6%) in edematous type, minimal infiltration(58.5%) in fibrous type and severe infiltration(69.3%) in infiltrative type. 5) The cells infiltrated are lymphocyte, plasma cell, histiocyte, neutrophile, eosinophile, monocyte and basophile. Most of cells infiltrated are lymphocyte and plasma cells and lymphocytes are observed in all slides.