Abstract: Objective To investigate the expression of macrophage migration inhibitory factor（MIF） in osteosarcoma， and explore the relationship between MIF and clinicopathological factors and prognosis. Methods Immunohistochemistry was applied to detect expression of MIF in 61 osteosarcoma tissues and 15 corresponding adjacent tissues（＞5.0cm at the outer edge of the tumor tissue）. The relationship between MIF expression and clinicopathological factors of osteosarcoma was evaluated by chi-square test. Survival was calculated by KaplanMeier method, and survival analysis was proceeded by Cox regression. Results The positive rate of MIF in osteosarcoma tissues was 62.3％， and in adjacent tissues was 33.3％. The difference was statistically significant（P=0.043）. The expression of MIF was significantly correlated with lung metastasis（P=0.006）， but not related with sex， age， location， clinical stage and pathological type. The threeyear survival rate of patients with MIF positive expression was lower than that of those with MIF negative expression（70.3% vs. 95.8%, P=0.019）. Cox proportional hazards regression analysis confirmed that Enneking staging was an independent prognostic facor of osteosarcoma， while MIF was not. Conclusion MIF may play an important role in metastasis in osteosarcoma， so might be employed to evaluate the prognosis of osteosarcoma patients.