The most common adverse effect of intravenous heparin is hemorrhage. Of the these, retroperitoneal hemorrhage and femoral neuropathy secondary to heparin anticoagulation has reported in 1966 for the first time by DeBolt and Jordan. We experienced a case of spontaneous retroperitoneal hemorrhage due to iliopsoas muscle hematoma in patient with myocardial infarction receiving intravenous heparin for a 3 days in therapeutic doses. The pathophysiology of iliopsoas muscle hematoma has not yet been cleared. But because of the possibility of large amount in volume, retroperitoneal hemorrhage has been known as a serious adverse effect that leads to the hypovolemic shock and death. In this article, we described the clinical manifestation, the importance of the early diagnosis and diagnostic clues and associated factors of the retroperitoneal hemorrhage in patient receiving intravenous heparin.