Purpose: This study aimed to determine the core competencies of Chinese gerontological nurse specialists and test the psychometric properties of a core competency self-evaluation instrument. Methods: This study consisted of 2 stages. A literature review, theoretical analysis, and the Delphi methods involving 28 experts were performed to identify the core competencies required of gerontological nurse specialists in China. Then, a self-evaluation instrument developed based on the results of stage I was tested among 225 certified gerontological nurse specialists. An exploratory factor analysis was applied to test the construct validity, and the content validity and reliability were also evaluated. Results: The core competencies of gerontological nurse specialists comprised 3 first-level domains, 9 second-level dimensions, and 69 third-level items. The average scale-level content validity, overall instrument’s Cronbach’s α, and test-retest reliability were 0.963, 0.983, and 0.834, respectively. The results of the exploratory factor analysis indicated that the factors in the 3 first-level domains (attitude, skill, and knowledge) explained 68.579%, 69.599%, and 75.872% of the variance, respectively. Conclusion: The results showed that the core competencies of Chinese gerontological nurse specialists were reliable and that gerontological nurse specialists could use this self-evaluation instrument to assess their core competencies.