Background and Aim: Strategic planning)SP) is the art and science of strategic analysis of an organization, forecasting changes in an organization's internal and external environments, setting strategic goals, developing suitable strategies, and allocating resources to achieve competitive advantage. Strategic planning plays an important role in enhancing hospital success. However, it has encountered various challenges in Iranian hospitals. This study aimed to identify the critical success factors)CSFs) of the strategic planning process in Iranian hospitals. Materials and Methods: This qualitative study was performed using semi-structured interviews with 47 members of the strategic planning committees of 17 hospitals in Tehran, Iran, in 2016. Thematic analysis was used for data analysis. Overall, 44 CSFs were identified for strategic planning and were grouped into 8 themes and 23 sub-themes. Results: Managers' belief in SP usefulness, SP justification, top managers' commitment to and involvement in SP, setting up a competent SP team, using an appropriate SP model conducive to hospitals' structure and culture, promoting teamwork and creativity, empowering employees to involve actively in SP, providing necessary financial and physical resources, setting up the information management and process management systems, and patient centeredness are key factors in SP success. Conclusion: The SP success depends on strong leadership and management, coherent planning, conducive organizational culture, organisational learning, and effective management of employees, customers, resources and processes.