Background Restoration of both normal movement of the pelvis and centre of mass is a primary goal of walking rehabilitation in post-stroke patients because these movements are essential components of effective gait.The aim of this study is to quantitatively analyze the effect of ankle-foot orthosis on walking ability,and to investigate the correlation between improvements in trunk motion and walking capacity.Methods Walking speed,centre of mass displacement,and pelvic movements were examined in 20 post-stroke hemiparetic patients with and without ankle-foot orthosis using three-dimensional motion analysis.Results Using ankle-foot orthosis improved walking speed,pelvic rotation and tilt,and lateral and vertical displacements of the centre of mass (P ＜0.01).Moreover,the gait asymmetry index was significantly decreased (P ＜0.01),and the Functional Ambulation Categories score improved significantly when patients used an anklefoot orthosis (P ＜0.05).There was significant correlation between improvements in the walking capacity and the displacement of the centre of mass in both vertical and lateral directions (P ＜0.01).Conclusions Using ankle-foot orthosis improves the walking capacity by improving the stability and concordant of the trunk in hemiplegic patients.The improvement in the walking capacity from using an ankle-foot orthosis may be attributed to its prevention of foot drop and compensation for the instability of the ankle joint.