BACKGROUND: There has been a growing body of research focusing on patients with Congestive Heart Failure (CHF) and chronic obstructive pulmonary disease (COPD) admitted to the intensive care unit (ICU). However, the optimal blood pressure (BP) level for such patients remains insufficiently explored. This study aimed to investigate the associations between systolic blood pressure (SBP) and in-hospital mortality among ICU patients with both CHF and COPD. METHODS: This retrospective cohort study enrolled 6309 patients from the Medical Information Mart for Intensive Care IV (MIMIC-IV) database. SBP was examined as both a continuous and categorical variable, with the primary outcome being in-hospital mortality. The investigation involved multivariable logistic regression, restricted cubic spline regression, and subgroup analysis to determine the relationship between SBP and mortality. RESULTS: The cohort consisted of 6309 patients with concurrent CHF and COPD (3246 females and 3063 males), with an average age of 73.0 ± 12.5 years. The multivariate analysis revealed an inverse association between SBP and in-hospital mortality, both as a continuous variable (odds ratio = 0.99 [95% CI, 0.99~1]) and as a categorical variable (divided into quintiles). Restricted cubic spline analysis demonstrated an L-shaped relationship between SBP and mortality risk (P nonlinearity < 0.001), with an inflection point at 99.479 mmHg. Stratified analyses further supported the robustness of this correlation. CONCLUSION: The relationship between SBP and in-hospital mortality in patients with both CHF and COPD follows an L-shaped pattern, with an inflection point at approximately 99.479 mmHg.