Congenital midline upper lip fistula is a very rare congenital anomaly that can be accompanied by other congenital abnormalities such as cleft lip and palate, and may appear as a symptom of a syndrome such as Pirre-Robin' s syndrome. It has been reported that this disease can be transmitted and presents signs of infection such as swelling of the upper lip, abscess formation, and pus discharge from the fistula. However, a case of infection in infancy has never been reported before. Here, we report a case of a six-month-old baby with an infected congenital midline upper lip fistula. The patient visited our hospital with swelling of the upper lip and suckling disorder. With the midline upper lip fistula infected, signs of infection such as swelling of the upper lip, pus discharge from the fistula, and domeshaped swelling of the oral vestibule of the maxillary anterior tooth were observed. Due to these acute symptoms, the patient had a suckling disorder. After anti-inflammatory treatment, we resected the lip fistula under general anesthesia. Congenital midline upper lip fistula is likely to cause infection in infancy, leading to a suckling disorder.Early examination and treatment for a congenital midline upper lip fistula is suggested.