Neonatal alloimmune thrombocytopenia(NAIT) is a very rare disease caused by maternal alloantibodies' response to neonatal platelet antigens. Because the most common cause of NAIT is incompatibility for platelet-specific antigens, NAIT cases due to anti-HLA antibodies are very exceptional. The patient was a second born female. She had no petechia or purpura at birth. But her platelet count was 55,000/mm3 and other laboratory findings were normal. On family history, the first baby had thrombocytopenia at birth too without petechia or other abnormal symptoms and his platelet count became spontaneously normal later. The mother's platelet count was normal and she had no history of idiopathic thrombocytopenic purpura(ITP) or bleeding tendency. Platelet crossmatching test showed positive between citric acid untreated paternal platelets and maternal serum, but negative to citric acid treated paternal platelets. These findings suggest maternal serum which contain anti-HLA antibodies to attack neonatal platelets and paternal platelets. Therefore this report documents a patient with neonatal thrombocytopenia induced by maternal anti HLA antibody.