The triggers of secondary thrombotic thrombopcytopenic purpura (TTP) include drug toxicity, radiation and high-dose chemotherapy, angioinvasive infections, surgery and acute graft versus host disease. TTP secondary to surgery have been reported in a number of cases. Most of the cases have been occurred after open heart surgery. Extensive endothelial damage is held responsible as the initiating mechanism in postoperative TTP cases. However, there is no report of secondary TTP describing development owing to ABO incompatible blood transfusion. Here, we describe a patient who developed TTP after transfusion of ABO incompatible blood during hospitalization for bypass surgery. We also propose a hypothesis which may account for the possible underlying mechanism.