Paroxysmal nocturnal hemoglobinuria(PNH) is an acquired hematologic disorder characterized by intravascular hemolysis, nocturnal hemoglobinuria, thrombotic events and bone marrow failure. It rarely occurs in children and can be complicated by acute renal failure(ARF). Here, we present two cases of ARF complicating PNH which has not been reported yet in Korean children. We suggest that PNH should be considered in differential diagnosis of ARF in children associated with intravascular hemolysis.