Thrombotic thrombocytopenic purpura (TTP) is a rare syndrome of unknown etiology and has a high mortality rate. TTP is characterized by a pentad of clinical findings, including microangiopathic hemolytic anemia, thrombocytopenia, renal abnormalities, neurologic signs and fever. The pathological feature of TTP consists of disseminated microvascular platelet thrombi. We describe a case of TTP with primary anti-phospholipid syndrome. A 27-year-old woman developed TTP in her second trimester of pregnancy. She presented with classical symptoms of TTP with compatible renal biopsy findings. Although four articles of SLE criteria (1982 ARA) were fulfilled, three of them were considered to be derived from multiple thrombosis except for a positive antinuclear antibody. Positive antiphospholipid antibodies (lupus anticoagulant and anticardiolipin antibody) with SLE-like findings suggested the diagnosis of antiphospholipid antibody syndrome rather than SLE. Although TTP has been described in patients with SLE and they can share common clinical and pathological features, the relationship between these two diseases is controversial. Many theories have been proposed to explain the nature and cause of intravascular platelet aggregation in TTP. But the pathogenesis of TTP is still unclear. This case suggests an important causal relationship between antiphospholipid antibodies and TTP during pregnancy. In TTP patients who also have SLE or SLE-like features, the antiphospholipid antibodies may have a role in the development of multiple microthrombosis.