With the aid of phase contrast microscope the author studied the ciliated epithelial cells of the mucous membrane obtained from the maxillary sinus at the time of operation. The results were as follows: 1. It was possible to observe the form of the cells and cilia, basal bodies, nuclei, mitochondria, storage granules, Golgi's apparatus etc. without staining. 2. The ciliary movement was mainly shown in hooked type, its effective stroke, recovery stroke and metachronism were observed distinctly, but in few cases climbing movement was observed. 3. The ciliary movement became gradually inactive and finally ceased, and then nuclear memb- rane became brilliant and double-contoured with the lapse of time. Further, the cell showed a tendency of swelling and at last the protoplasm and niuclei were destructed, but in few cases contraction of the cells was observed. 4. Studying the effect of various chemicals and durgs upon the ciliated epithelial cells, it was confirmed that fixatives produce distinct changes for living cells. Distilled water showed marked influence on the cells where normal saline did not show any significant change.