Mineralocorticoid receptor antagonists (MRAs) constitute a beneficial therapy in chronic heart failure, but their use in the acute heart failure (AHF) setting remains rather unexplored. To assess the effect of MRAs administered during hospitalization on in-hospital outcomes of patients with AHF, we performed a post-hoc analysis of the Acute Heart Failure Global Registry of Standard Treatment (ALARM-HF). Patients of the original study cohort (n = 4953) were categorized according to in-hospital MRA treatment status as MRA-treated (n = 1439) and untreated (n = 3514) subjects. Nearest-neighbor propensity score with 1:1 matching yielded a subsample of pairs of MRA-treated and MRA-untreated patients (n = 1003 in each treatment group) that were balanced in an extensive list of baseline characteristics. In-hospital mortality between MRA-treated and untreated patients were assessed by Cox regression analysis before and after adjustment for known prognostic factors and other concomitantly administered intravenous and oral HF specific therapies. In the matched cohort, in-hospital mortality was 4.2 vs 10.8% in MRA-treated vs untreated patients. Treatment with MRAs was associated with a reduction of in-hospital mortality [HR 0.372 (95% CI, 0.261–0.532), p < 0.001]. This association remained significant after adjustment for known prognostic factors and co-administered intravenous and oral HF therapies [HR: 0.618 (95% CI, 0.383–0.995), p = 0.048]. In conclusion, MRA therapy administered during hospitalization for AHF was associated with reduced in-hospital mortality. The role of MRAs in AHF deserves further examination in adequately powered randomized controlled studies.