Understanding the formation and behavior of wear debris at friction interfaces in polymers is essential for enhancing the performance and durability of polymer-based mechanical systems. However, conventional observation techniques have limited our ability to capture the dynamic processes underlying debris generation. To overcome this, top-view in-situ scanning electron microscopy (SEM) imaging of friction interfaces using a microtribometer combined with an electron-transparent silicon nitride (Si 3N 4, hereafter referred to as SIN) thin film was developed. In this study, in-situ friction tests were performed between a SIN film and a polyacetal (POM) pin. The in-situ SEM observations revealed that wear debris originates from stretching, tearing, and detachment of the POM surface due to adhesive interactions. Repeated friction also caused sections of a thick transfer layer to be torn away. When a suitable gap existed between the SIN film and the POM pin, fragments rolled and formed rolled debris. Additionally, the formation of a freestanding layer sliding between the SIN film and the POM pin, initiated by internal crack propagation and detachment within the POM was observed. These dynamic phenomena, complex to capture using conventional techniques, offer new insights into polymer wear mechanisms, highlighting the importance of transfer layer dynamics, surface deformation, and interfacial geometry in debris formation.