This study was designed to investigate the effects of an ankle foot orthosis(AFO) with variable ankle joint angles on balance performance in healthy adults. Eighteen healthy adults were recruited in this repeated measures design with subjects as their own controls. An AFO with four kinds of ankle joint angles(-5, 0, 5, and 10 degree) were used and balance performance was measured during single limb standing. Three trials were obtained and then averaged for data analysis. Foot pressure was measured using an F-scan system and muscle activity was measured using an MP150 system. There were significant differences in balance performance with ankle joint angles. An AFO with -5 degrees was associated with significant increases in postural sway(anterior-posterior), and in muscle activity for the medial gastrocnemius and tibialis anterior compared with other degrees of angle. Findings of this study show that angles of an AFO are related to balance performance and a joint angle of 10 degree is effective for promoting joint stability and postural control. This information can be used by clinicians to prescribe AFOs.