Abstract: Objective To study the correlation between imaging manifestations of intramedullary osteosarcoma of extremities after neoadjuvant chemotherapy and gross specimens. Methods MRI was performed after three courses of large dosage chemotherapy for 17 patients with intramedullary osteosarcoma of extremities admitted to our department from September 2005 to December 2006.Gross specimens were taken by cutting along the coronal axis and stored in 10% formalin for X-ray and CT examination.Imaging manifestations and pathological findings of the specimens were compared. Results X-ray,CT and pathological examinations showed a difference in length of osteosarcoma（P＜0.05）.However,MRI and pathological examination showed no difference in length of osteosarcoma before operation（P＞0.05）. Conclusion Osteotomy can be performed 2 to 3cm beyond the margin since MRI shows a relatively small error of the invasion of osteosarcoma.