Objective: This study aimed to investigate the association between the change in the National Early Warning Score (NEWS) before and after interhospital transport and the survival of critically ill patients transported by critical care transport. Methods: A retrospective analysis of SMICU (Seoul Mobile Intensive Care Unit) transfer records and the National Emergency Department Information System (NEDIS) was conducted. Adult patients who used SMICU from 2016 to 2018 were included. Trauma patients and post-cardiac arrest patients were excluded. The NEWS before departure from the transferring hospital and the NEWS before the arrival at the receiving hospital were extracted, and the difference between both NEWS (△ NEWS) was calculated. The △ NEWS was categorized into three groups: -2 or less, -1 to 1, and 2 or more. The primary outcome was 24-hour post-transport mortality. Multivariable logistic regression was applied to calculate the adjusted odds ratio (AOR) and 95% confidence interval (CI) for the outcomes. Results: Of the total number of 1,837 patients, 1,065 patients were included. △ NEWS were -2 or less in 131 (12.3%), -1 to 1 in 805 (75.6%), and 2 or more in 129 (12.1%) of the patients. The 24-hour mortality rate was 3.1%, 2.9%, and 7.0% in the △ NEWS≤-2, -1≤△ NEWS≤1, and △ NEWS≥2 groups, respectively. Relative to -1≤△ NEWS≤1, the AORs for the 24-hour mortality were 1.11 (95% CI, 0.38-3.29) in △ NEWS≤-2 and 2.56 (95% CI, 1.15-5.70) in △ NEWS≥2. Conclusion The changes in NEWS in critical care interhospital transport are associated with patient prognosis.