A 31-year-old pregnant woman with no remarkable past medical history presented with mild hypoxemia, which worsened after she underwent cesarean section. To determine the cause of hypoxemia, we performed chest computed tomography after the cesarean section and found a pulmonary arteriovenous fistula of the A10-V10 shunt in the lower lobe of the right lung and V10 had expanded to 12 mm. Forty-nine days after giving birth, the patient underwent thoracoscopic right lower lobectomy. The results of blood gas analysis improved after surgery; before surgery, the partial pressure of oxygen was 66.4 Torr, which increased to 98.4 Torr after surgery. The patient was discharged on the ninth day after surgery. 　　Pulmonary arteriovenous fistula may be exacerbated by changes in cardiac output and circulating blood volume during pregnancy. If hypoxemia progresses after pregnancy, pulmonary artery fistula must be identified.