The hemangiopericytoma originated from the greater omentum is a very rare vascular tumor and grows to a large mass without symptoms for a long period. The diagnosis can be made on ultrasonogram, CT or MRI and angiogram with the findings of well circumscribed, solitary mass with hypervascularity in the abdominal cavity especially retroperitoneal cavity. The surgical treatment is recommended due to its possibility of malignant potential and metastasis on diagnosis. The evaluation of differential diagnosis to rule out this tumor is obligatory if a large solitary movable mass being palpated in abdomen. We experienced a case of hemangiopericytoma of greater omentum which was diagnosed as a left ovarian tumor preparatively, and we report the case with brief review of the literatures.