We investigated the incidence of pulmonary embolism after total hip or knee arthroplasty. Arterial pO2 while the patient was breathing room air was measured at pre-operative day and 5 post-operative day using a Blood Gas Analyzer. Selection of patients for perfusion/ventilation scan during this study was dependent on the results of arterial blood gas determination that was more than 10 mmHg depression Of arterial pO2 level after surgery. More than depression of that was occurred in 11 patients (17.7%). Eight of them (72.7%) detected abnormalities (V/Q mismatch) in perfusion/ventilation scan, and we diagnosed them PE. More than 70% of PE was detected by only estimating the pre and post-operative arterial pO2. It was concluded that the estimation of arterial pO2 (pre and post-operation) was useful for the detection of PE, and combining estimation of arterial pO2 with the clinical feature evaluation method, low-invasive diagnosis and rapid treatment should be possible.