Abstarct: The purpose of this study was to determine the effect of value co-creation in online communities of football club brands on fans’ identification and social capital. This study was quantitative and practical research. The statistical population of this study was the entire followers of two Instagram pages for Persepolis and Esteghlal football clubs. The minimum sample size was calculated using Gpower software, according to which 190 fans were selected as a sample by voluntary sampling method. For data collection, Lin and Lu’s (2011) social capital questionnaire, Mael and Ashforth’s (1992) identification questionnaire, and Hsieh’s (2015) value co-creation questionnaire were used. The face and content validity of the questionnaires were examined and confirmed by sports management experts and the reliability of the questionnaires using Cronbach's Alpha coefficient, composite reliability, and factor loadings. The collected data were analyzed using two categories of descxriptive and inferential statistics methods. In order to test the hypotheses, the method of structural equations modeling with the partial least squares approach was used. Data analysis was done using SPSS.26 and Smart-PLS.3 statistical software. The results showed that value co-creation has a positive and significant impact on both fans' identification and social capital. Also, social capital influenced fans' identification positively and significantly. In addition, value co-creation had a positive and significant impact on the fans’ identification through mediating role of social capital. Therefore, it is recommended for clubs to invest in their virtual pages and online communities to provide fans with the opportunity to more interact with each other and the club. This helps clubs to use the capacity, knowledge, and information of fans to improve their services and influence the consumption behavior of fans.