Background. To evaluate the association between blood urea nitrogen (BUN) to creatinine (Cr) (BUN/Cr) ratio and the in-hospital mortality of critically ill patients with cerebral infarction in intensive care unit (ICU). Methods. In this cohort study, the data of 3059 participants with cerebral infarction were collected from the Medical Information Mart for Intensive Care (MIMIC)-III and the MIMIC-IV database. After propensity score matching (PSM) on age and gender, 2085 people were involved in and divided into the alive group ( n = 1390 ) and the dead group ( n = 695 ) based on the results of follow-up. Multivariate logistic analyses were applied to identify the confounders and the association between BUN/Cr and mortality of cerebral infarction. Results. The median follow-up time was 10.5 days. Among 2778 participants, 695 were dead at the end of follow-up. Univariate analysis revealed that BUN/Cr [ risk   ratio   RR = 1.01 , 95% confidence interval (CI): 1.01-1.02] might be associated with the in-hospital mortality of cerebral infarction patients. After adjusting for respiratory failure, malignant cancer, anticoagulation, liver disease, white blood cell (WBC), red cell distribution width (RDW), glucose, bicarbonate, and temperature, BUN/Cr had week correlation with the increased risk of in-hospital mortality of cerebral infarction patients ( RR = 1.01 , 95% CI: 1.01-1.02). Conclusion. This study evaluated the association between BUN/Cr and the in-hospital mortality of cerebral infarction patients in ICU and found that BUN/Cr had weak correlation with the increased risk of in-hospital mortality of patients with cerebral infarction in ICU especially in males and those with respiratory failure, malignant cancer, and without liver disease, as well as those receiving anticoagulation.