Encouraging stakeholder participation is now considered an appropriate approach to green space improvement. The main question is how to have people participate in the improvement process. This study aims to propose a participatory stakeholder management model of green space improvement in Tehran Metropolis. Therefore, 190 of Tehran Municipality's green space experts were selected as the statistical population for in-person and field interviews. The dependent research variable was defined as the green space improvement measured in four dimensions (i.e., green space planning, green space designing, green space implementation, and green space maintenance). However, the independent variable included the aspects of participatory management (i.e., participation in goal-setting, participation in decision-making, participation in organizational change, participation in problem-solving, and organizational culture). The results indicated that only organizational culture and participation in organizational change explained nearly 96% of participatory management variations and improved 67% of the green space.