Choanal polps usually present as large, soft gelatinous masses in the nasopharynx. Most of the choanal polyps arise from mucosa of the maxillary sinus near the natural ostium of the sinus. Recently we treated a patient with choanal polyp originated from the left sphenoid sinus. We present that case with review of literatures. An 18-year-old female patient had complained of nasal obstruction bilaterally, mucoid rhinorrhea and foreign body sensation in the nasopharynx since 6 years before. Posterior rhinoscopy showed huge polypoid mass in the nasopharynx. The C-T scan revealed soft tissue mass shadow originated from antero-lateral wall of the left sphenoid sinus. The lining mucosa of left maxillary sinus was healthy and natural ostium was patent by the sinoscopic examination. The polyp was removed by means of intranasal approach under the local anesthesia. The specimen was proved to be chronic inflammatory polyp microscopically.