Thrombocytopenia occurred after 17 days of administration of vancomycin (VCM) in 2 cases of MRSA pneumonia. The drug lymphocyte stimulation test using VCM and anti-platelet antibody were negative for these 2 cases. However, platelet bound IgG significantly increased and the total number of immature megakaryocytes in the bone marrow increased. Corticosteroid administration after VCM was very effective for thrombocytopenia. In case 1, thrombocytopenia occurred three times after using of VCM, suggesting to have been induced by VCM. The mechanism of thrombocytopenia was immunological destruction. It has been reported that VCM-induced neutropenia might be induced via an immunological mechanism. We reported here 2 cases of thrombocytopenia induced by VCM, which is frequently used for MRSA pneumonia.