Social media are an integral part of modern society and they have become a big industry especial-ly after the emergence of social medias on Mobile devices. It has been a while that most Small and Medium Enterprises (SMEs) have used social medias to promote their business activities. Social medias also supply different facilities for SMEs to help them explore their services on the market. This is more evident for those SMEs whose activities are more project based. The pur-pose of this paper is to find out important factors influencing on building brand using social me-dias for SMEs. The study designs a questionnaire in Likert scale and distributes it among 238 of SMEs’ experts in food industry in city of Tehran, Iran. Using principle component analysis, the study has determined that acquiring knowledge from social media, market approach in mass me-dia, market reaction approach in media, strategic mass media capability and social status influ-ence the most on building brand in SMEs.