Stiff Person syndrome (SPS) is a rare, disabling syndrome characterized by progressive muscle stiffness and axial rigidity. It may have an autoimmune, paraneoplastic or cryptogenic etiology. A 59-year-old woman presented with stiffness and involuntary spasms in the lower extremities. In a neurologic examination, lower extremity and axial rigidity were revealed. Anti-glutamic acid decarboxylase antibody was negative, anti-amphiphysin was antibody positive. She was diagnosed as having SPS. The symptoms were improved after intravenous immunoglobulin and cancer therapy.