Purpose: Today, the online purchase intention can create a competitive advantage for the organization and social media marketing activities can be effective in this field. Therefore, the purpose of this study was to determine the effect of social media marketing activities on the online purchase intention of sportswear customers according to the mediating role of the company's brand. Methodology: This research based on the purpose was a practical and based on the nature was a cross-sectional from type of descriptive. The population of this study was the sportswear customers of different brands in Mazandaran province who used social media to buy products. The sample size based on the Krejcie and Morgan table was determined 384 people who these people were selected by available sampling method. The tool of the current research was a 32-item researcher-made questionnaire with three dimensions of social media marketing activities (9 items), online purchase intention (2 items) and company's brand (21 items and 4 components of brand loyalty, brand experience, brand attitude and customer-brand relationship). The content validity of the researcher-made questionnaire was estimated at 0.75 by 8 professors and their reliability was estimated ranged from 0.65 to 0.83. Data were analyzed by structural equation modeling In SPSS-V25 and Smart.PLS-V24 software. Findings: The results of this study showed that there was a positive and significant correlation between the most variables of social media marketing activities, brand loyalty, brand experience, brand attitude, customer-brand relationship and online purchase intention (P<0.05). Also, the model of social media marketing activities on the online purchase intention of sportswear customers according to the mediating role of the company's brand had a good fit, and in the mentioned model, the variable of social media marketing activities on the brand loyalty, brand experience, brand attitude and customer-brand relationship and the variables of brand loyalty, brand experience, brand attitude and customer-brand relationship on the online purchase intention had a direct and significant effect and the variable of social media marketing activities with the mediating of brand loyalty, brand experience, brand attitude and customer-brand relationship on the online purchase intention had an indirect and significant effect (P<0.05). Conclusion: Social media marketing activities directly and indirectly through company's brand impact on the online purchase intention. Therefore, to improve customers' online purchase intentions can be improved the social media marketing activities and company's brand.
