This study was conducted with the purpose of identifying the dimensions and validating an organizational capacity‑building model aimed at enhancing human resource productivity. The research was applied in purpose and adopted a mixed‑method approach in its execution. In the qualitative phase, purposive sampling was employed, and semi‑structured interviews were conducted with 19 academic and executive experts in the fields of organizational capacity building and human resource productivity until theoretical saturation was reached. The interview data were analyzed through thematic analysis, resulting in the extraction of basic and organizing themes.In the quantitative phase, the statistical population consisted of all employees of Karaj Municipality in 2024. Stratified random sampling was applied, and data were collected using a researcher‑developed questionnaire designed based on the qualitative findings. Instrument validity was assessed using internal consistency, and reliability was evaluated through Cronbach’s alpha coefficient. Data analysis was performed at both descriptive and inferential levels, including confirmatory factor analysis, using SmartPLS version 3.The results indicated that the organizational capacity‑building model for improving human resource productivity is grounded in five fundamental dimensions: individual capacity building, process capacity building, institutional capacity building, cultural and organizational learning capacity, and governance capacity. These dimensions encompass components such as the development of professional knowledge and skills, enhancement of motivation and job satisfaction, innovation and continuous improvement, participatory leadership, strengthening technological infrastructure, sustainable financial support, inter-organizational collaboration, promotion of a learning-oriented culture, reinforcement of ethical values and organizational trust, and alignment with legal frameworks and macro‑level policies. Overall, the findings demonstrate that implementing this model can effectively pave the way for improving human resource productivity within Karaj Metropolitan Municipality.