Background: Decisional involvement “is the pattern of distribution of authority for decisions and activities that govern nursing practice policy and the practice environment, Staff nurse decisional involvement can improve quality of patient care as well as nurses' Job satisfaction. There is also evidence that decisional involvement improves the nurse work environment , commitment, perceived empowerment, self-growth, organizational development ,patient and organizational outcomes, and employee well-being. Aim of study: the study aimed to identify factors affecting decisional involvement among staff nurses. Subjects and methods: A cross- sectional analytic design was used. The study was conducted in Mobart EL Mahalla Hospital; it is affiliated to General Authority for Health Insurance, western branch. Simple random sample that included 150 out of 250 staff nurses. Two data collection tools were used to carry out this study namely, Decisional involvement scale (DIS) and decisional involvement Factors questionnaire. Results: The highest percentage of staff nurses viewed actual decision-making is made by administration. While more than three quarter of them viewed that decision making decisions should tend more towards sharing and nurse led rather than administration. The highest percentage of staff nurses had high level agreement upon the organizational factors affecting decision making ,compared with minority of the study participants had agreement regarding the items personal factors. Conclusion: The highest percentage of staff nurses of administration were actually group that makes units decisions with minimal involvement of nursing. The staff nurses view of the organizational factors that affecting their involvement in decision making is much higher in comparison with their view of personal factors. Recommendation: The rules and regulation governing decision making in the hospital and who should be involved should be revised to give more room to staff nurses' involvement. The decision making in matters closely related to nursing work should primarily led by nurses, examples are the areas of staffing and recruitment and quality of nursing support staff. Hospital administrators with help of nurse managers should conduct periodic assessment of staff nurses' views of actual decisional involvement. Head nurse and nurse supervisors should periodically involve staff nurses in decision making at the unit level and for simple matters to foster their abilities and encourage their decisional involvement. Staff development and training officers in the hospital should provide adequate training in decision making for staff nurses to enhance their involvement.