This is a case report of delayed hemolytic transfusion reaction due to Anti-Le*b and Anti-JK*b in treatment of multiple fracture. The patient was a 14 year-old boy and had no history of transfusion or blood products. The patient underwent open reduction and internal fixtion for fracture of supracondyle of femur with massive blood transfusion. Abnormal finding of ABO incompatibility was not found as usual method. The patient developed a marked fall in hemoglobin and hematocrit value and a marked hyperbilirubinemia at 8 day after surgery, which suggested hemolytic anemia and jaundice. After the evaluation of this hemolytic anemia and jaundice, we found the anti-Le*b antibody and Anti-Jk*b antibody. A delayed hemolytic transfusion reaction represents an infrequent, but potentially hazardous complication of blood transfusion. The phenomenon usually oringinates from exposure to a blood group antigen by prior transfusion or pregnancy. delayed appearance of isoantibodies, first detected 4 to 14 days after the transfusion of apparently compatible blood, has been detected by the authors.