This study aims to investigate the role of citizen participation in enhancing the environmental quality of Mashhad using a descriptive research design and inferential statistical analyses. To this end, the key components of participatory planning were prioritized through a survey of experts. Subsequently, an urban citizen participation model was developed based on in-depth interviews. The statistical population consisted of the citizens of Mashhad. The study area covered Districts 1, 5, and 11 of Mashhad. A survey method and questionnaire were employed to collect data from residents of the selected districts. The findings suggest that the distribution of institutional and citizen participation indicators is not uniform across the selected districts with varying levels of environmental quality. District 5, despite having a diverse range of welfare, educational, and recreational facilities, generally demonstrates higher levels of participation at both the institutional and citizen levels. In contrast, District 11, as a developing district, exhibits moderate levels of participation at both levels. District 1, as one of the central and older districts of the city, demonstrates a moderate level of institutional participation and a high level of citizen participation. The observed regional differences in the levels of institutional and citizen participation are associated with variations in socioeconomic indicators, population density, educational attainment, and accessibility. The results highlight the importance of considering regional differences in planning and policymaking aimed at enhancing public participation and improving urban environmental quality. Given the differences in institutional and citizen participation across areas with varying levels of environmental quality, adopting policy and urban management approaches tailored to the specific conditions of each district is essential.