AIMS: To develop and evaluate a novel Diuretic Intensity Score (DIS) and investigate its relationship with mortality in hospitalized heart failure patients. METHODS: We analyzed propensity-matched data from two independent cohorts: MIMIC-IV (n = 15 942) and the China Regional Heart Failure Database (n = 1884). DIS was calculated based on diuretic types, routes, and combinations. Primary and secondary outcomes were 28- and 90-day all-cause mortality. RESULTS: Higher DIS was significantly associated with reduced 28-day mortality (Severe vs. Mild: HR 0.27, p < 0.001 in MIMIC-IV; HR 0.10, p < 0.001 in Chinese cohort) and 90-day mortality. Restricted cubic spline analysis revealed an inverse, non-linear relationship, with mortality risk decreasing as intensity increased and then plateauing. CONCLUSIONS: In this propensity-matched analysis of two independent cohorts, a higher DIS was associated with lower 28- and 90-day all-cause mortality in hospitalized heart failure patients. Given the observational design, these findings should be regarded as hypothesis-generating associations rather than evidence of a causal benefit and require confirmation in prospective randomized trials before any change in clinical practice can be recommended.