The effect of two different types of functional ankle-foot orthosis on the gait of patients with spastic hemiplegia was studied. A gap was cut into the conventional stiff orthosis to allow a limited dorsiflexion of 10-15°, while plantarflexion was blocked (spring type). This gap was bridged by an aluminum bar to stiffen the orthosis for the experiment. Fourteen patients of different ages (6.5-20.1 years) walked barefoot and with the orthosis, once springy and once stiff. Kinetics and kinematics were analyzed. Gait was significantly improved into normal pattern by using any type of ankle-foot orthosis. While walking barefoot with a toe-heel-toe gait, the physiological heel-toe gait was restored with any type of orthosis. The spring type of orthosis was significantly superior to the stiff orthosis. This was most clearly expressed in the general parameters of gait-like cadence, velocity, and step length. Kinetic data gave a significant improvement by using any ankle-foot orthosis. Whereas break force was similar with both types, push-off was further improved with the spring type. Kinematics revealed little statistical difference between the two types, although gait was more dynamic and physiological with the spring type of orthosis. Any functional ankle-foot orthosis ameliorates the gait pattern in patients with spastic hemiplegia, but a spring type of orthosis renders the gait more dynamic and best corrects the pathology of gait.