The present study aims to provide a sociological explanation of the impact of social media platforms on the formation of urban protest movements, with a particular emphasis on the mediating role of online social capital. Drawing upon resource mobilization theory and social capital theory, this research was designed to elucidate how digital interactions within social networks can enhance the capacities for political and social mobilization. The study employed a descriptive-analytical approach based on a survey method. The statistical population comprised active users of social media platforms (Instagram, Telegram, and Twitter) residing in the metropolitan area of Tehran, from which 350 participants were selected using a non-probability purposive sampling technique. Data were collected through a researcher-developed questionnaire and analyzed using SPSS and SmartPLS software. The findings revealed that the use of social media platforms had a significant positive effect on individuals’ willingness to participate in urban protest movements (β=0.302, p<0.001). Additionally, online social capital played a significant mediating role in this relationship (β=0.512, p<0.001), and extensive use of these media considerably enhanced trust, network cohesion, and participatory norms among users (β=0.573, p<0.001). These results indicate that beyond their informational functions, online social capital plays a crucial role in organizing and reinforcing solidarity among protest actors. The study underscores the importance of multilayered analyses of digital interactions and recommends that policymakers develop media literacy programs and create civic dialogue platforms to better manage the unintended consequences of networked mobilization capacities.