[Purpose] The purpose of the study was to assess the muscle activity change of the tibialis posterior, flexor digitorum longus, and peroneus longus during gait with orthoses. [Subjects and Methods] Sixteen healthy males participated in this study. Activity of each muscle was measured by using fine-wire and surface electromyography. Gait task was performed by the participants barefoot, with footwear and with orthoses. The electromyography data from a stance phase of each gait trial were used for analysis. The stance phase was divided into contact, midstance, and propulsion phases. The data from ten participants were extracted for final analysis, as electromyography measurements were unsuccessful for the other six. [Results] The results demonstrated that orthoses significantly reduced the tibialis posterior muscle activity in the propulsion phase compared to that in the barefoot condition. Although there was a significant difference in the midstance phase, post hoc analysis did not indicate significant differences among the phases. No significant electromyography amplitude change was detected in flexor digitorum longus and peroneus longus. [Conclusion] Orthothes reduced the tibialis posterior activity level during gait. This result may be beneficial for patients with injuries related to excessive activity of tibialis posterior.