Background: Evaluation of nursing educator's competencies is a prerequisite to the quality assurance of nursing education. Using standardized evaluation tool to assess core competencies of nurse educator is essential to prepare and promote their role competence and excellence in nursing education. Aim: This study aimed to assess the applicability of developed evaluation tool for nurse educator core competencies. Subject and Methods: A methodological cross-sectional design was used in carrying out the study on Two groups namely jury group consists of (35) members and Nurse educators group, their total number is (37). Setting: The study was conducted at two selected Technical Institutes of Nursing affiliated to Ain-Shams Specialized Hospital and Ain-Shams University Hospitals. Data was collected using the following three tools which were developed by researcher and used to conduct this study namely; Opinionnaire sheet, Questionnaire Sheet and Observation Checklist. The results, showed that the developed evaluation tool can be applied to assess core competencies of nurse educators as it was applied in different ranges were from (51%- 81 %). Conclusion: The developed evaluation tool was applied in the study setting where they are urgently needed. Observation of nurse educator's application of the core competencies revealed that there was deficiency in some areas of nurse educator's assessment, planning, implementation, evaluation and documentation.  Recommendations: It was recommended to implement the developed evaluation tool in other setting, and conduct training session for nurse educator regarding core competencies.