Background: Short foot exercise, which is an intrinsic foot muscle exercise proposed by the foot core system, is used to improve the strength of intrinsic foot muscles and sensory input and function of the foot. However, there is a lack of studies that assessed the improvement in foot function after short foot exercise in patients undergoing rehabilitation after a modified Broström operation of the ankle joint. Objectives: To investigate the effects of short foot exercise on intrinsic foot muscle cross-sectional area and balance ability in patients who had undergone a modified Broström operation of the ankle joint. Design: A single blind, randomized controlled trial. Methods: Sixteen patients who were undergoing ankle rehabilitation exercises following the modified Broström operation were randomized into two groups. General physical therapy, short foot exercises, and ankle rehabilitation programs were performed in the experimental group (n=8), whereas general physical therapy and ankle rehabilitation programs were performed in the control group (n=8). For outcome measures, the intrinsic muscles of the foot were imaged using the Sonimage HS1 musculoskeletal ultrasound system. The Y-balance test and RS-foot scan system were used to confirm dynamic balance ability and static balance ability. Results: The cross-sectional area of the abductor hallucis and dynamic balance ability significantly improved in the experimental group that underwent short foot exercise compared to the control group (P<.05). In contrast, static balance ability was not significantly different between the two groups (P>.05). Conclusion: Short foot exercise successfully increased the cross-sectional area of the abductor muscle and improved dynamic balance after a modified Broström operation