Background: The low medial arch in the flatfoot is caused commonly by dysfunction of the tibialis posterior muscle resulting abnormal shape of the foot. Although abnormal joint shapes of the flatfoot have been reported, there is a paucity of information on the temporal kinematics of individual joints in flatfoot subjects. Previously, there were several studies that investigated the kinematic changes in the flatfoot using reflective markers that were attached on the foot. However, the motion capture system could not obtain the bone motions happening under the skin. Moreover, none of those studies investigate the relative movements on the articulating joint surfaces. This study aims to quantify and compare the arthrokinematics in the ankle, subtalar and midtarsal joints in flatfoot subjects during walking using bi-planar fluoroscopic system