In this study, we examined a technique for maximizing the wear resistance of a polyurethane film composited with plasma-treated carbon nanotubes (CNTs). In our previous work, we showed that adding plasma-treated CNTs enhanced the wear resistance of off-the-shelf polyurethane. Here, we also investigated the chemical reactions between polyurethane and plasma-treated CNTs. The result showed that plasma-treatment modified isocyanate groups on CNTs possibly react with polyols to form urethane. However, the off-the-shelf polyurethane was supposed to have limited polyols because urethane reactions were mostly finished. In the present study, we synthesized polyurethane ourselves in order to compare how the timing of synthesis of plasma-treated CNTs into polyurethane (either before or after urethane reactions occur) impacts resulting films. Five polyurethane films were prepared, including a film composited with plasma-treated CNTs synthesized before urethane reactions (in situ polymerized CNT-composite polyurethane film). A wear-resistance test was then conducted to evaluate the mechanical properties of the composite films. The results showed that the plasma-treated CNTs enhanced wear resistance by a factor of two. Next, we conducted a tensile test to examine how the wear resistance was enhanced in polyurethane films composited with plasma-treated CNTs. The tensile test showed that in situ polymerized plasma-treated CNTs significantly improved Young's modulus of CNT-composite polyurethane. These combined results suggested that plasma-treated CNTs should be composited into polyurethane before urethane reactions occur to maximize the wear resistance of composite polyurethane. Published under an exclusive license by the AVS.