PURPOSE: This study aimed to determine the responsiveness of the Brazilian version of the Identification of Functional Ankle Instability (IdFAI) questionnaire in students who received an eight-week treatment for chronic ankle instability (CAI). METHODS: Twenty-five college students (aged 23.12 ± 2.80 years) with CAI, as identified by the IdFAI questionnaire, were recruited. We used distribution and anchor-based methods to assess the responsiveness of the questionnaire, and its ability to determine clinical changes in participants. Eleven anchors were used: Visual Analog Scale for instability (VAS-i); Cumberland Ankle Instability Tool (CAIT); Isometric dorsiflexion, plantar flexion, inversion, and eversion muscle strength measured using a manual dynamometer; Dynamic balance as assessed through the Star Excursion Balance Test (SEBT-Y); Active ankle dorsiflexion range of motion as measured using the weight-bearing lunge test; and Functional performance assessment using three hop tests: single hop, triple crossover hop, and side hop. The distribution-based method used effect size (ES) and standardized response mean (SRM), whereas the anchor-based method used paired -tests. Both methods allowed the calculation of the minimal important difference (MID). RESULTS: The Brazilian IdFAI showed high responsiveness, with a large magnitude of change (ES = 1.34) and a high responsiveness index (SRM = 1.28) when assessed after a treatment for CAI. The IdFAI total score ( < .001) and all the 11 anchors [VAS-i ( < .001); CAIT ( < .001); Isometric dorsiflexion ( < .001), plantar flexion ( < .001), inversion ( < .001), and eversion ( < .001) muscle strength; SEBT-Y ( < .001); Lunge test ( = .002); Single hop ( < .001); triple crossover hop ( < .001); and side hop tests ( < .001)] showed significant differences. The anchor and distribution-based methods demonstrated MID values of 3.72 and 1.49-2.27, respectively. CONCLUSION: The Brazilian IdFAI questionnaire is a patient-reported outcome measure sensitive to clinical changes in individuals with CAI. It can be used as an identification of patients with CAI, and as a parameter to verify clinical changes of clinical trials or therapeutic interventions in the population with CAI.