Activities of daily living (ADL) are important prognostic factors for heart failure. The functional independent measure (FIM) has emerged as a comprehensive valid measure of ADL from both physical and cognitive perspectives. This study aimed to investigate the prognostic impact of the FIM score on clinical outcomes in hospitalized patients with acute decompensated heart failure (ADHF). We retrospectively analyzed 473 ADHF patients, with available pre-discharge FIM scores, admitted to our institution between May 2018 and May 2020. Primary outcome measures, defined as a composite of 180-day all-cause deaths and readmissions, were compared among three tertiles. The median FIM score was 102 (interquartile range: 85-115). Tertile 1 corresponded to an FIM score > 111 (n = 154), Tertile 2 to that of 90-111 (n = 167), and Tertile 3 to that of < 90 (n = 152). During follow-up, 28 deaths and 114 readmissions occurred. Patients with lower FIM scores were associated with a graded increase in the risk of primary outcome measure (p = 0.001). Even after multivariable adjustment, the results remained significant [Tertile 1 vs 3; adjusted hazard ratio: 3.28 (95% confidence interval: 1.72-6.56), p < 0.001; Tertile 2 vs 3; 2.32 (1.27-4.47), p = 0.006]. FIM scores were significantly associated with readmission or death within 180 days of discharge in hospitalized ADHF patients.