We attempted to evaluate postoperative maxillary sinus mucosal changes in 20 maxillary sinuses of 16 patients who underwent functional endoscopic sinus surgery (FESS). Ciliated area of the maxillary sinus mucosa and ostium of maxillary sinus were quantitatively observed by scanning electron microscope and image analysis before and after FESS. In the present study, the number of preoperative ciliated cells of maxillary sinus mucosa and ostium was significantly reduced, goblet cells and microvillous cells were increased, and squamous cell metaplasia observed in part of the maxillary sinuses. Many damaged ciliated cells tend to recover and ciliated area significantly increased at 6-12 months after the surgery. The results showed that the damaged ciliated epithelium could return to normal by the improvement of ventilation and drainage of the maxillary sinus following FESS.