Purpose While existing research has enhanced our understanding of job and work environment characteristics that promote middle managers’ entrepreneurial behavior, recent studies have begun to explore the psychology behind the development of such behavior. This study enriches such research by examining whether middle managers’ psychological ownership (PO) mediates the relationship between their involvement in strategy development and their entrepreneurial behavior. Design/methodology/approach The results are based on a survey of 176 middle managers in Germany. Data analysis rests on partial least squares structural equation modeling. Findings The findings reveal that PO only mediates the relationship between middle managers' content-related involvement in strategy development and their entrepreneurial behavior, while this does not hold for their process-related involvement. Originality/value This study contributes to prior literature by providing a more fine-grained understanding of the psychology underlying middle managers’ entrepreneurial behavior. It is the first to highlight the role of strategy involvement and PO in this process.