Objective: To observe and analysis the effect of ankle foot orthosis(AFO) on lower extremity stability, weight loading ability and range of joint motion(ROM) of the knee and ankle during walking. Method:Twenty patients with foot drop had taken part in this study.There were 6 cases with assist walking and 14 cases with independent ambulation. All patients received evaluation of walking ability,lower extremity activity ability and balancing function of body in wearing or unwearing AFO. Five cases wearing AFO received gait analysis about 1 month later.Result:The main lower extremity capability of the patients(such as walking speed, step width and downstairs time,etc) wearing AFO hadn′t improved greatly(P0.05); The patients′ balancing stability of body wearing AFO had improved greatly(P0.05); The ROM of the knee and ankle of the patients during walking had been improved(P0.05,P0.01).Conclusion:An effect of AFO on lower limb function of the patients is to improve foot drop and knee excessive extension,to increase balancing stability of the body and lower extremity. Changes in ADL and gait weren′t found.Author′s address Department of Rehabilation Medicine, First Affiliated Hospital of Nanjing Medical University, Nanjing,210029