Myoepithelioma is a rare tumor of the salivary glands. Occurrence of myoepithelioma in the nasal cavity is even rarer, and there has been no case wherein the change in the size of the tumor was confirmed by imaging. In this report, a 84-year-old female was found to have a rapidly enlarged tumor on the preoperative image, but she had shown no significant size change in a medical examination six months ago or in the paranasal sinuses view three months ago. The image showed a rapid increase in the size of the cystic component, so the endoscopic medial maxillectomy was performed. There was no recurrence of the tumor at follow-up six months after surgery. Although myoepithelioma is rarely found in the maxillary sinus of the sinonasal cavity, it is important to suspect myoepithelioma and consult a pathologist if it shows a similar pattern to the current case.