Antiphospholipid syndrome (APS) is an uncommon prothrombotic disorder that has been increasingly recognized in recent years. The diagnosis of APS must be associated with venous or arterial thrombosis or both. Patients with APS usually present with recurrent deep vein thrombosis, pulmonary thromboembolism, thromboembolic stroke, or myocardial infarction. Here, we report a case of a 61-year-old female who presented with a 3-month history of increasingly frequent retrosternal chest tightness. After treadmill test and thallium-201 myocardial perfusion scan, she was admitted and underwent elective coronary angiography but developed acute thrombosis after direct intracoronary stenting. She was successfully rescued with repeat percutaneous transluminal coronary angioplasty and prolonged heparin and glycoprotein IIb/IIIa antagonist use. Laboratory data showed prolongation of partial thromboplastin time and positive anti-cardiolipin antibody. These findings satisfied the criteria for APS; the patient was diagnosed with primary APS because she had neither typical symptoms nor signs of systemic lupus erythematosus or other immunologic disorders. Thereafter, long-term oral anticoagulant appeared to be effective. To our knowledge, this is the first report of acute stent thrombosis in a patient with primary APS.