Objective To explore the effect of medial UKA surgery on restore the knee kinematics.Methods: Nine patients who received fixed-bearing medial UKA consented to participate in this study. All patients completed pre-surgical (3 weeks before) and post-surgical (7±2 months) testing (5 M, 4 F; average age 62.3 ± 5 years). Synchronized biplane radiographs were collected at 100 images per second during three repetitions of a chair rise movement . Motion of the femur, tibia, and implants were tracked using an automated volumetric model-based tracking process that matches subject-specific 3D models of the bones and prostheses to the biplane radiographs with sub-millimeter accuracy . Anatomic coordinate systems were created within the femur and tibia and used to calculate tibiofemoral kinematics . Additional outcome measures included the center of contact in the medial . The results of the three movement trials were averaged for each knee in each test session. Results: The UKA knee was in 4.8° more varus than the contralateral knee prior to surgery （P=0.001）. After surgery, the UKA knee was in 3.1° more valgus than before surgery（P=0.012）. The UKA knee was 4.4° more externally rotated than the contralateral knee prior to surgery (p=0.004) . However, our data showed that the medial tibia contact center of the UKA knee has moved posteriorly 2.5 mm compared to the contralateral knee (p=0.016). There was no different in lateral compartment joint space before and after surgery. Conclusion UKA could improve the varus of the knee joint and restore the rotation biomechanical characteristics of the knee. The lateral compartment joint space didn’t changed before and after surgery. The center of closest contact in the medial tibia compartment of the UKA knee was changed after surgery.