The prognostic nutritional index (PNI) and serum chloride level are related to adverse outcomes in patients with heart failure. However, little is known about the relationship between the PNI and serum chloride level in predicting the poor prognosis of patients with acute decompensated heart failure (ADHF).We reviewed 1221 consecutive patients with ADHF admitted to the First Affiliated Hospital of Kunming Medical University from January 2017 to October 2021. After excluding patients with in hospital death, missing follow-up data, missing chloride data, missing lymphocyte (LYM) count data, or missing serum albumin data, 805 patients were included. PNI was calculated using the formula: serum albumin (ALB) (g/L) + 5 × LYM count (10^9/L). Patients were divided into 4 groups according to the quartiles of the PNI, and the highest PNI quartile (PNI Q4: PNI ≥ 47.3) was set as the reference group. The patients in the lowest PNI quartile (PNI Q1: PNI < 40.8) had the lowest cumulative survival rate, and mortality risk decreased progressively through the quartiles (log-rank χ2 142.283, P < 0.0001). Patients with ADHF were divided into 8 groups by quartiles of PNI and median levels of serum chloride. After adjustment, the hazard ratio (HR) for all-cause mortality in ADHF patients in Group 1 was 8.7 times higher than that in the reference Group 8. Furthermore, the addition of serum chloride level and PNI quartile to the Cox model increased the area under the Receiver operating characteristic (ROC) curve by 0.05, and the area under the ROC curve of the new model was higher than that of the original model with traditional risk factors.Both the lowest PNI quartiles and low chloride level indicate a higher risk of all-cause death in patients with ADHF.© 2024. The Author(s).