Supervision is one of the techniques used to improve nurses’ competencies as; it provides essential support for nurses progressing into advanced practice to foster professional development, and career adaptability. Aim: The present study aimed to evaluate the effect of educational program about clinical supervision for first line managers on staff nurses' career adaptability. Research Design: Quasi experimental design was utilized. Study Setting: the study was conducted in all units at Benha University Hospital, the total number of the studied units were (57) units. The study sample was: All the available head nurses and their assistants (88), and convenient sample of staff nurses (176) who are working in the abovementioned study setting. Tools of data collection: Three tools were used: (1) Clinical Supervision Knowledge Questionnaire, (2) Observational checklist of first line managers' performance, and (3) Career Adapt-Abilities Scale (CAAS). Results: The findings of this study showed that there was a highly statistical significant improvement in first line managers' knowledge and performance regarding clinical supervision thorough program. Moreover, there was a highly statistical significant improvement in staff nurses' level of career adaptability. Conclusion: The study concluded that there was a highly statistical positive correlation between first line managers' clinical supervision performance and staff nurses' career adaptability. Recommendations: Setting clear responsibilities for both nursing supervisor and supervisee through a constructive clinical supervision policies and procedures, providing supportive healthy work environment that help nurses to reflect on their personal and professional work-related issues with their clinical supervisors that help in enhancing their career adaptability, and integrating career adaptability in nursing education