This systematic review aims to examine the factors that impact the sustainability of open educational resources (OER) initiatives. A total of 226 articles from the Web of Science, ERIC and SCOPUS databases were subjected to content analysis to identify factors that influence the sustainability of OER initiatives based on the 3M (macro, meso and micro) framework. Our findings reveal that OER sustainability is influenced by different factors in different contexts, such as platform, content creator, learner, learning material and institutional setting. Within the institutional context, institutional policies categorised as a macro and meso factor, were identified as the most frequently mentioned factor affecting OER sustainability. The factors of providing institutional support and incentives were identified as meso factors. For faculty and learners, meso and micro factors such as attitude, motivation, awareness of OER, time, ICT needs and digital literacy were frequently mentioned. Access emerged as a prominent meso factor within the OER platforms dimension. Quality was identified as a critical macro and meso factor for the sustainability of OER. After the quality factor, material-related factors such as licensing, interactivity and free access emerged. Finally, an OER sustainability framework is proposed along with recommendations for researchers, practitioners and administrators to promote sustainable OER practices.