This research investigated the relationship between supplier integration and customer integration on operational performance by mediating supply chain flexibility in SMEs in Indonesia. The method used in this research used quantitative methods using a conceptual framework and analysis of research data was performed using structural equation models (SEM) with SmrtPLS 3.0 software tools. Respondents to this study were 650 SMEs owners in Indonesia who were determined using the simple random sampling method. Data collection in this study was carried out on primary data in the form of respondents' statements obtained from answers to online research questionnaires designed using a Likert scale of 7. The results of this study stated that Supplier Integration had a positive and significant effect on supply chain flexibility. Customer Integration had a positive and significant effect on Supply Chain Flexibility. Supply Chain Flexibility had a positive and significant effect on operational performance. Supplier integration had a positive and significant effect on operational performance. Customer integration had a positive and significant effect on operational performance.