Introduction: The need to design and establish an integrated knowledge management system is one of the strategic issues of the social security organization. The present research was conducted with the aim of developing a model of Internal organizational factors effective on tacit knowledge management of social security organization with the Grounded Theory approach. Methods: The current study is of a qualitative type that was conducted with the Grounded Theory method. The statistical population of this research included managers at the high, middle, and operational levels of the vice-chancellor of management and human resources and the subordinate offices of this vice-chancellor in the headquarters of the Social Security Organization in 1401. The sampling method was purposive & snowball. Using the principle of theoretical saturation, the number of samples reached 18 semi-structured interviews. In the present study, to measure the validity of the findings, content validity was used and to measure the reliability of the findings, the method of reviewing the interview texts by the interviewees and the method of two coders was used. Data analysis was done with open, axial, and selective triple coding using MaxQDA. 12 software. Results: 57 open codes, 5 central codes including organizational strategy, information technology governance, organizational structure, organizational culture, and learning organization, 18 selective codes including knowledge sharing, external environment, innovation, foresight, analytical, reactive, personal abilities, mental patterns, shared vision and ideals, team learning, systems thinking, complexity, formality, centralization and decentralization, acquisition, planning, monitoring, and support were identified. Conclusions: The components of causal conditions include knowledge sharing, external environment, and innovation, context including formality and complexity, intervention conditions including acquisition, planning, monitoring, and support, phenomena including concentration and lack of concentration, strategies including foresight, analysis, and reaction, and consequences. It included the ability of personal abilities, mental patterns, shared vision and ideals, team learning, and systems thinking. It is suggested that the officials of the social security organization provide a suitable platform for the management of tacit knowledge in the social security organization by considering the designed model.