Objective To investigate feature of lateral collateral ankle ligament injury and appearance of post-treatment on MRI, and evaluate its clinical diagnostic value. Methods MRI examinations of 106 cases with lateral collateral ankle ligament injury were retrospectively analyzed. Among all patients, 74 cases were proved by operation, other 32 cases were proved by clinical therapy, follow up and the recovery condition about posttreatment by MRI. Results We can see the appearance of lateral collateral ankle ligament injury on MRI: Grade Ⅰ, the ligaments showed enlargement and hyperintense on T2 wigthed imaging. Grade Ⅱ of slight and severe, the ligaments showed enlargement or diminution, with interruption of partial ligament, s continuity (rupture less than 1/2 on grade Ⅱ of slight, rupture larger than 1/2 on grade Ⅱ of severe), heterogeneous hyperintense on T2 wigthed imaging. Grade Ⅲ, ligaments showed interruption of whole ligament, s continuity, and the broken end show irregular, and the joint have major hydrops. Other injury can be seen with lateral collateral ankle ligament injury. Patients of post-treatment were examined by MRI, we can evaluate therapeutic effect by grade 0-Ⅲ. Conclusion MRI is the best method which comprehensive evaluate therapeutic effect, it can provided full information for clinical diagnosis and treatment.