Transplant-associated thrombotic microangiopathy is a bothersome complication in terms of morbidity and mortality after allogeneic stem cell transplantation. It is believed that the endothelial injury causes to thrombotic microangiopathy, but the pathogenesis is not known completely. Although there is a consensus about diagnostic criteria, there is no concurrence for the treatment particularly. Even though thrombotic microangiopathy is considered by transplantation physician recently, adequate prospective multi-center studies and broad serial cases are not presented yet.