A　serial　assistive　mechanism　was　proposed　for　the　hip　adduction/abduction　and　flexion/extension　motion　assistance,　which　is　kinematically　compatible　with　human　hip　complex.　As　the　mechanism　is　connected　to　the　wearer,　a　2-degree-offreedom　human-robot　closed　chain　is　formed.　The　closed-form　position　solution　of　the　assistive　mechanism　was　investigated,　the　Jacobian　matrixes　which　map　the　velocity　and　force　from　the　active　joint　space　of　the　assistive　mechanism　to　hip　joint　space　were　derived,　and　five　new　indices　for　performance　evaluation　of　the　assistive　mechanism　were　defined.　On　the　basis　of　the　presented　position　solution　and　evaluation　indices,　the　performances　of　the　assistive　mechanism　during　a　human　gait　cycle,　such　as　the　human-robot　motion　offset,　the　motion　and　force　assistive　characteristics,　were　analyzed　through　the　examples　with　seven　wearing　error　models.　The　results　show　that　the　assistive　mechanism　has　several　distinct　advantages　including　small　human-robot　motion　offset,　favorable　motion　assistive　isotropy,　and　high　force　assistive　efficiency.　The　proposed　indices　can　evaluate　the　assistive　feature　adequately,　and　the　serial　assistive　mechanism　is　applicable　to　the　2-degree-of-freedom　hip　adduction/abduction　and　flexion/extension　motion　assistance.