Nowadays, everyone who is involved in virtual space hears the phrase of “Social Networks” more than anything. These networks have occupied most of the web space. According to Alexa web site ranking, the most visited internet web sites are social networks. Almost in all real environments, the talk is about the contents of the news and information provided by social networks. Actually what are these social networks? What sort of features do they have? Why internet providers have turned to use social networks? What specifications and capacities do these social networks have so attract such a huge internet providers?The more important of all, what sort of benefit do the public relations institutions as media and communication providers in governmental / Non-governmental corporations, organizations and ministries receive? To what extent is it possible to use the capacities and capabilities of these networks to accomplish the missions of public relations and fulfill its objects in an organization? Is it possible to provide an applicable and practical model for the public relations in order to use capacity of virtual social networks? These were the questions in the mind of researcher made him to study about virtual social networks and their role and applications in the institution of public relations. The method used for this research is the survey. The tools for measuring the function of virtual social networks in the institution of public relations from the perspective of the activists in the field of Public Relations” is researcher made questionnaire which include 34 questions. The research illustrates functions of virtual social networks in the fields of advertisement, branding, opinion polling, polling, researches, the content of media policy, media and news activities, and illustration in the institution of public relations and the related organization, while it attempts to study and explain strengths and weaknesses of the function of these networks for the institutions of public relations.