Introduction: One of the basic competencies to become a professional nurse is clinical performance. Therefore, many studies use tools modified and supplemented by Choi to measure the clinical performance of nursing students, but there is no tool to measure the core competencies of nursing students. Aim/Objectives: This methodological study tested the reliability and validity of a self-report instrument measuring the core competencies of nursing students. Internal consistency, reliability, and construct validity were assessed using confirmatory and exploratory factor analysis. Methods: Questionnaire data was collected from 249 nursing students at four universities in J province, South Korea, from August 20 to September 30, 2020. Results: The core competencies showed reliable internal consistency, with a Cronbach__ampersandsignrsquo;s alpha of 0.90 for the total scale. Factor loadings of the 32 items on seven subscales ranged from 0.53 to 0.88, and three factors explained a total variance of 66.22%. The seven subscales model was validated by confirmatory factor analysis (root mean square residual 0.90). Conclusions: The results demonstrate that the instrument is useful in measuring the core competencies of nursing students.