Clinical manifestations of pulmonary embolism are nonspecific during anesthesia. A 44 years old female received elective operation for right tibio-fibular fracture under spinal anesthesia. During operation, the patient received oxygen supply 5 L/min via mask with oxygen. On arrival of postanesthetic care unit, oxygen saturation of pulse oxymeter (SpO2) was 89% and with the 100% oxygen 10 L/min by mask, SpO2 went up rapidly to 100%. When the patient breathed under room air, SpO2 suddenly decreased to 80%. Chest x-ray at that time was non-contributory. Under the suspicion of pulmonary embolism, the patient was transferred to intensive care unit (ICU), and low molecular weight heparin (LMWH) treatment was started. LMWH was changed to regular heparin on the second day of ICU admission after conclusive diagnosis with spiral computed tomography and lung perfusion scan. The patient's oxygenation progressively improved and on the 10th day of ICU, the patient was transferred to general ward and she was discharged without any sequelae on the 23th day postoperatively.