Objective To evaluate the imaging characteristics of chondromalacia patellae(CMP)in low-field MR and the value of MR in diagnosis.Methods 37 cases with CMP proved by arthroscopy and/or operation were carefully examined by 0.3 Tesla permanent magnet MR unit.The results of MRI were retrospectively analyzed according to that of arthroscopy and operation to search for the MR imaging manifestations of different degrees of patellae cartilage injuries in CMP.Results According to the golden-standard by arthroscopy and operation as for CMP,the overall diagnostic accuracy of MRI was 79.4%,with 28.6% accuracy in the early phase,92.6% in the late phase of CMP.Conclusion Low-field MR imaging is accurate in diagnosing CMP in the late phase and should be suggested as a useful nontraumatic imaging modality in the assessment of CMP before arthroscopy and operation.