Abstarct: The purpose of this research is to determine the effect of social media marketing electronic word of mouth of sports customers of sports stores with a mediating role of trust and brand attachment. The research method is descxriptive-applied. The statistical population of the study consisted of followers of sports equipment stores in cyberspace (Instagram) and 243 people were selected as a sample by available sampling method. Questionnaires used to collect data included SEO and Park Social Media Marketing Questionnaire (2018), SEO and Park electronic word of mouth (2018), Trust in Brand Shahin et al. (2013), and attachment to Brand Dennis et al. (2016). To determine the face and content validity of the questionnaires, the opinions of 8 experts and professors of sports management were used. The reliability of the questionnaires was evaluated in a pilot study on 22 members of the research community through Cronbach's alpha coefficient equal to 0.90, 0.82, 0.84, and 0.93. The results of data analysis showed that the effect of social media marketing on customer trust (0.64), brand attachment (0.53), and electronic word of mouth (0.52) is positive and significant; Also, the effect of both variables of trust and brand attachment on electronic word of mouth is positive and significant (with 0.30 and 0.20, respectively); Brand trust also has a positive and significant effect on brand attachment of customers of sports stores (0.39). The indirect effect of social media marketing on electronic word of mouth is positive and significant through both brand trust (0.27) and brand attachment (0.17). Generally, it is possible to build trust and attachment to the brand through interaction with customers on social media, followed by positive advertising for the sports store.