[Purpose] This study examined the effects of an ankle-foot orthosis worn during balance training on lower limb muscle activity and static balance of chronic stroke patients. [Subjects] The subjects were twenty-five inpatients receiving physical therapy for chronic stroke. [Methods] The chronic stroke patients were divided into two groups: thirteen patients were assigned to the ankle-foot orthosis group, while the remaining twelve patients wore only their shoes. Each group performed balance training for 20 minutes, twice per day, 5 days per week, for 6 weeks. The lower limb muscle activities of the paralyzed side tibialis anterior, medial gastrocnemius, and the stability index were measured before and after the 6-week intervention. [Results] Comparison of the groups indicated a significant difference in the muscle activity of the paralyzed side tibialis anterior and the stability index of the eyes-open standing position. After the intervention, the ankle-foot orthosis group evidenced a significant difference in the muscle activities of the paralyzed side tibialis anterior and paralyzed side medial gastrocnemius as well as the stability index of the eyes-open standing position, eyes-closed standing position, eyes-open standing position on a sponge, and eyes-closed standing position on a sponge. The group that only wore their shoes showed significant differences in the stability indexes of eyes-open standing and eyes-open standing on a sponge. [Conclusion] Using the ankle-foot orthosis was effective during the initial training of lower limb muscle activities and the static balance training of chronic stroke patients. However, it was not effective for a variety of dynamic situations.