Social media have provided brand-new capacities for affecting users, and leading them toward social action. The aim of the current research was to develop a model of factors affecting opinion leadership of social media users in creating social action. To this end, a correlational design was adopted to describe the relationship between predictor varibels of leader’s reputation and attractiveness, expertise, normativity, social status, similarity to users, official media, message characteristics, the users’ influenceability, and criterion variable of dissemination of calls for social action, and simultaneous social action on Instagram social media. A researcher-developed questionnaire which its validity and reliability were confirmed, was filled out by 393 participants. Cronbach’s Alpha for all sub-scales, except for one, was greater than .70. The current research findings showed that opinion leadership on social media did not directly affect the simultaneous social action of users, rather, its influence was mediated by opinion leader’s “reputation and attractiveness”, “users’ influenceability”, and “dissemination of calls for social action”. Also, “message characteristics” had the greatest effect on the opinion leadership. The findings can be employed by educational and scientific centers, and institutions responsible for contect production and dissemination, to create simultaneous social action through opinion leadership.