<p>In the context of emerging markets, small and medium-sized enterprises (SMEs) face substantial pressures to transition toward circular economy models, as they often encounter significant limitations in organizational capacity and institutional support. This study aims to examine how organizational culture influences sustainable performance in SMEs in Vietnam. It specifically investigates the mediating role of circular economy practices and the moderating effect of circular economy entrepreneurship in this relationship. A quantitative research design was employed using survey data collected from 355 middle and senior-level managers of SMEs. The data were analyzed through structural equation modeling (SEM) using SmartPLS version 3 to test the hypothesized relationships. The results consist of three important parts. First, circular economy entrepreneurship moderates the relationship between organizational culture and circular economy practices, leading to long-term sustainability. Second, circular economy practices mediate the relationship between organizational culture and sustainable performance. In addition, organizational culture also has a direct and positive effect on both circular economy practices and sustainable performance. These results suggest that fostering a sustainability-oriented culture and entrepreneurial orientation toward circularity can enhance SMEs’ sustainable performance. This study contributes to the literature by developing and empirically validating an integrated model that connects organizational culture, circular economy practices, and sustainable performance. It highlights the critical role of internal organizational drivers in promoting sustainability and offers practical insights for SMEs in emerging economies seeking to embed circular principles into their business strategies.</p>