A 40-year-old woman was scheduled for abdominal hysterectomy. Moderate difficulty in tracheal intubation was expected on preoperative evaluation. A size 3 laryngeal mask airway (LMA) was inserted after the induction of general anesthesia. The LMA insertion was accomplished smoothly at the first attempt and there was no air leakage during manual ventilation. Soon after the insertion, acute swellings were noted in the bilateral submandibular triangle regions. Enlargement and deformity of the submandibular glands were diagnosed by ultrasonography. The enlargements increased with elevated pressure of the LMA cuff, but disappeared completely in five minutes after removal of the LMA. Such enlargement did not occur with subsequent tracheal intubation. The patient had an uneventful postoperative course without any residual sequelae. We should pay attention to possible submandibular gland swelling by LMA insertion.