BackgroundPostural instability and gait abnormalities are frequently observed after an ankle sprain. A modified Four Square Step Test (mFSST) was developed to assess dynamic balance during gait. The aim of this study was to evaluate the reliability and validity of the mFSST in individuals with ankle sprains.MethodsThe study included 39 individuals with grade 1 and 2 ankle sprains with a mean age of 30.36 ± 6.21 years. The dynamic balance of the participants was assessed with the mFSST and Timed Up & Go test (TUG). To determine the test-retest reliability of the mFSST, the test was repeated approximately 1 h apart.ResultsThe test-retest reliability of the mFSST was excellent (ICC = 0.85). Furthermore, when the concurrent validity of the mFSST was examined, a high correlation was found between with the TUG (r = 0.78, p < 0.001).ConclusionThe mFSST is a valid and reliable clinical assessment method for evaluating dynamic balance during walking in individuals with ankle sprains. We think that the mFSST is preferable in clinical evaluations because its platform is easy to prepare and requires very little equipment.