Abstract: Objective To investigate the diagnostic value of magnetic resonance imaging (MRI) for lower limb osteosarcoma by comparing the findings between X-ray and MRI. Methods Fifteen surgically or pathologically confirmed patients with lower limb osteosarcoma (11 males and 4 females) underwent both plain and enhanced MRI (with CT scanning in 4 cases) in addition to radiography, and the findings were compared. Results The diagnostic accuracy of both MRI and X-ray film was 100%. Compared with X-ray, MRI was capable of clear display of the lesion extent, perpendicular periosteal reaction, the two layers of Codman’s triangle and the skip lesions. Conclusion Plain X-ray film provides a convenient and practical diagnostic modality for lower limb osteosarcoma, but MRI has better performance in clearer display of the tumor range and identification of early-stage lesions.