We studied the effect of Kami-kihi-to (Jia-Wei-Gui-Pi-Tang) on the production of autoantibodies in ten patients with chronic immune thrombocytopenic purpura. After administration of Kami-kihi-to, platelet count was increased in seven of the ten patients (p < 0.05). Using Western blotting, we demonstrated the disappearance of autoantibody reaction with antigen in one patient. However, platelet-associated IgG was decreased in eight of ten patients (p < 0.05). Kami-kihi-to appears to promote the suppression of autoantibodies in patients with chronic immune thrombocytopenic purpura. No side effects were observed in any patient. Thus, Kami-kihi-to may be a useful and safe drug in the management of chronic immune thrombocytopenia purpura.