In the sharing economy, a notable surge in irresponsible consumption behaviours can be observed, attributed primarily to consumers’ absence of ownership over shared assets. This study, which is grounded in psychological ownership theory, investigates whether customization can enhance socially responsible consumer behaviour (SRCB) through the lens of psychological ownership (PO) within the sharing economy. A moderated mediation model is developed, and four experimental studies confirm that customization significantly fosters SRCB in shared contexts, with psychological ownership serving as a pivotal mediator. (...) Moreover, service proactivity moderates the impact of customization on psychological ownership such that high service proactivity does not further enhance PO for customized products/services and, consequently, SRCB. This paper not only expands the scope of research on the mechanisms driving SRCB in the sharing economy but also offers insights into consumer ethics by highlighting fostering consumer responsibility for both shared resources and collaborative consumers to ensure the sustainable development of the sharing economy, thereby contributing to the broadening of the business ethics discourse on consumer accountability. (shrink)