This study aimed to examine the prognostic value of C-reactive protein (CRP)/albumin (ALB) ratio among patients who were admitted to the intensive care unit (ICU) in predicting 30-day mortality rate. This retrospective cohort study was conducted by examining the medical records of adult patients who were admitted to the ICU at Seoul National University Bundang Hospital between 1 January 2012 and 31 December 2016. Data from 6,972 individuals were included in the final analysis, and 547 of these individuals (7.1%) died within 30 days after their ICU admission. The multivariable Cox regression analysis revealed that an increase of 1 for the CRP/ALB ratio was associated with an 11% increase in the risk of 30-day mortality (hazard ratio: 1.11, 95% confidence interval: 1.09-1.14, P < 0.001). However, the area under curve of CRP/ALB ratio in receiver operating characteristic analysis was lower than that of Acute Physiologic Assessment and Chronic Health Evaluation (APACHE) II, Charlson comorbidity index, or serum albumin alone. Although an elevated CRP/ALB ratio on ICU admission was an independent risk factor for 30-day mortality rate, the predictive power of CRP/ALB ratio was lower than that of albumin alone, APACHE II, and Charlson comorbidity index.