Abstract Aims Chronic heart failure (CHF) is often a common comorbidity in critically ill patients admitted to the intensive care unit (ICU) and carries an extremely poor prognosis. The study aimed to investigate the relationship between the blood urea nitrogen to serum albumin ratio (BAR) and the prognosis of patients with CHF admitted to the ICU. Methods and results This retrospective cohort study included 1545 critically ill patients with CHF as a diagnosed comorbidity admitted to the ICU deposited in the MIMIC-III database, of whom 90 day all-cause mortality was 27.6% (n = 427) and in-hospital mortality was 17.3% (n = 267). The results of multiple logistic regression analysis indicated that BAR is an independent risk factor for in-hospital mortality in critically ill patients with CHF [compared with BAR ≤ 0.83; 0.83 < BAR ≤ 1.24: odds ratio (OR) 2.647, 95% confidence interval (CI) 1.797–3.900, P < 0.001; BAR ≥ 1.24: OR 3.628, 95% CI 2.604–5.057, P < 0.001]. Multiple COX regression analysis found a relationship between BAR and all-cause mortality at 90 day follow-up (0.83 < BAR ≤ 1.24: OR 1.948, 95% CI 1.259–3.014, P < 0.003; BAR ≥ 1.24: OR 1.807, 95% CI 1.154–2.830, P < 0.01; BAR ≤ 0.83 as a reference). Kaplan–Meier curves also showed similar results as well (P < 0.001). The areas under the receiver operating characteristic curves for predicting in-hospital mortality and 90 day all-cause mortality were 0.622 and 0.647, respectively. Conclusions BAR is an independent risk factor for in-hospital mortality and 90 day mortality in critically ill patients with CHF admitted to the ICU.