Abstract: The nurse manager offers crucial leadership for safe work, settings, and maintaining the best environment for achieving high quality of patients' outcomes, these to achieve the organizational objectives. The improvement of skills, that it is often underestimated, where the nurse managers are vital to success. Strive nursing leaders as providers during their job transfer from a clinical place. Aim of the study: To assess nurse managers' competencies and its relation to their leadership styles. Setting: This study was conducted at the Oncology Center, Mansoura University. A descriptive correlational research design was utilized. Subjects: The sample was composed of all nurse managers who are working during data collection (n=65). Tools: 1) Nurse Managers competency inventory (NMCI), and 2) Nurse Managers leadership styles. The results revealed that more than half of nursing managers demonstrate a high level of domain conduct daily unit operations, while, slightly less than half of study nurse managers had a low level of total competency and the higher mean scores of transformational leadership style were observed which the nurse manager always uses the idealized influence. The study concluded that there is a highly statistically significant relation between the nurse manager's competencies and the leadership style nursing managers.The study recommended that management, competency development introduced & emphasized within the nursing curriculum; also an orientation management training program to be developed and conducted for new nurse managers regarding leadership, management functions and required skills, as well as how they deal with different situations