Background: Post-COVID-19 functional capacity is one of the most impaired sequelae. Identifying the underlying conditions of post-COVID-19 functional impairments, assessed with six-minute walk test (6MWT) is needed. Aim:To identify predictors of altered post-COVID-19 functional capacity after 6 months. Methods:A prospective study conducted from May to September 2021 in a medical ICU including COVID-19 acute respiratory distress syndrome (ARDS) survivors who performed 6MWT six months after discharge. Reduced 6MWT is defined by walking distance <500 meters. Univariate and multivariate analyses were used to identify factors associated with reduced 6MWT. Results: Seventy COVID-19 patients were discharged alive. Among them 48(68.6%) patients performed 6MWT. At ICU admission, 38(77.6%) had moderate to severe ARDS, median Charlson score and respiratory support duration were: 0[0-1] and 6[4-8] days. Three months after discharge, 13(26.5%) patients had residual fibrosis in chest CT-scan and 11(22.4%) patients had moderate to severe baseline dyspnea (mMRC 3 or 4). Reduced 6MWT distance was found in 13(26.5%) patients. Factors associated with reduced 6MWT distance on univariate analysis were: Charlson score (p=0.001), moderate to severe ARDS (p=0.038),duration of respiratory support (p=0.033), mMRC3-4 (p<10-3) and residual fibrosis (p<10-3). On multivariate analysis, independent predictive factors of reduced 6MWT distance were: mMRC3-4 (OR, 56; 95% CI, [4.54-690.18]; p=0.002) and residual fibrosis (OR, 27.06; 95% CI, [2.52-290.34]; p=0.006). Conclusion: In critically-ill COVID-19 survivors, mMRC 3-4 and residual fibrosis are predictive factors of altered post-COVID functional capacity measured with 6MWT