Ankle Foot Orthosis (A.F.O) should endure the uncountable repeating impact and fatigue loadings owing to the gait characteristics. This study investigates the impact deflection and relationship between the absorbed energy and the residual strength rate using the glass/epoxy and the aramid/epoxy for the leaf spring in A.F.O. In conclusion, an equation was suggested to evaluate the absorbed energy and the residual strength rate by the different impact velocities. When the glass/epoxy and the aramid/epoxy was selected for the leaf spring in A.F.O, it was reasonable to use the glass/epoxy of the cross-ply for the parts subject to the large impact and the aramid/epoxy of the woven type for the parts to require the high elastic energy such as the large deformation.