This case showed that pulse oximeter was helpful for early detection of pulmonary edema during Cesarean section in a parturient woman with preoperative ritodrine treatment. Though arterial oxygen saturation ( Sp02 ) by pulse oximeter was low before the induction of anesthesia, the woman was anesthetized due to emergency situation. SpO2 was continuously low during the operation, so pulmonary edema was suspected. After the operaton, pulmonary edema was diagnosed on the chest x-ray. On the ECG, anteroseptal wall ischemia was detected. Supplementary O2 and diuretics therapy were performed. On the 3rd postoperative day, arterial blood gas analysis was within normal range. Four days after the operation, ECG was normalized and chest x-ray finding was much improved. 10 days later, chest x-ray finding was normalized.