Protein S is a cofactor for activated protein C in degradation of factor Va and VIIIa. Deficiency of protein S increases the risk of venous thrombosis and pulmonary thromboembolism. We report a case with isolated protein S deficiency who developed acute pulmonary thromboembolism after a routine coronary angiography. A 35-year-old woman was referred for evaluation of exertional chest pain. Coronary angiography was done by right femoral artery approach. After removal of compressive dressing, she suddenly felt dyspnea. Pulmonary thromboembolism was diagnosed by immediate transthoracic echocardiography and dynamic chest CT. Thrombolysis with urokinase and heparinization was done successfully. After 6-month-warfarinization, test for evaluation for hypercaogulable state was done. Total protein S antigen, free protein S antigen and protein S activity were all decreased. Protein C activity and mass, antithrombin III, anticardiolipin test, lupus anticoag-ulant antibody, antiphospholipid antibody, factor V Leiden mutation test, fibrinogen, FDP, and homocyteine levels were all normal.