This study aimed at determining decision-making styles used by nurse managers at main Assuit university hospital, and the effect of these styles on technical nurses' job performance. Methods: the sample consisted of 96 technical nurses and 35 nurse managers from medical and surgical units, the data collected using structured questionnaire form and technical nurses' performance evaluation sheet. Results: The highest percentage of nurse managers were used authoritarian, and the lowest used delegative decision making style. Performance of technical nurses working with nurse managers who used authoritarian decision-making style was significantly effective in care planning and evaluation of patient condition, while with nurse managers who used participative decision making style was significantly effective in all dimensions except evaluation of patient condition. Lastly, with nurse managers used delegative decision making style staff was significantly effective in implementation of patient care and their role in education Recommendation Arrange for meetings on regular basis between nurse managers and employees and nurse managers and director of nursing to give feed back about employees' performance.[Amaal S. Mohammed. Magda E. Nassar Soad A. Ghallab. Sahar M. Morsy. Nurses Managers' Decision Making styles and It's Effect on Staff Nurses' Job Performance. J Am Sci 2013; 9 (12): 170-179].(ISSN: 1545-1003). http://www. jofamericanscience. org. 22