Objective:The purpose of the present study was to describe a test to evaluate the maintenance of posture by measuring the inter-foot distance (IFD) during tandem stance. Methods: The subjects were 38 young healthy volunteers (age 29 ± 6 years, 17 men). A three-dimensional motion analysis system and a split-belt treadmill were used to collect data. The subjects allowed their front leg to move across the front of their body according to the treadmill belt movement. The maximum IFD was defined as the IFD when either foot was removed from the treadmill belt while the subject maintained a standing posture. Measurements were made under four conditions: the dominant and non-dominant leg placed in front of the body and treadmill belt velocities of 0.5 and 1.0 km/h. Data were analyzed using two-way analysis of variance. Results: The normalized maximum IFD was 10-12% of subject height. There was no significant interaction between the front leg and the treadmill belt velocity (P=0.42). There was a significant main effect of the front leg on the normalized maximum IFD: the normalized maximum IFD was larger when the dominant foot was in front of the body than when the non-dominant foot was in front of the body (P=0.044). There was no significant main effect of the treadmill belt velocity on the normalized maximum IFD (P=0.97). Conclusion: The normalized maximum IFD was significantly affected by which leg was placed in front.