Nano-composites of montmorillonite/polyimide (PI) were prepared by insitu polymerization. The mechanical properties, tribological performances and thermal stability of PI composites with different montmorillonite content were investigated. The wear surfaces of PI composites were observed by the scan electron microscope to analyze the wear mechanism. The results show that the addition of montmorillonite can improve the thermal stability of the composite material. With the increasing of montmorillonite content, the tensile strength of the composites is shown a downward trend, but the elastic modulus is increased significantly. The tribological performances of the PI composites are significantly improved when adding suitable montmorillonite. Along with increasing of the montmorillonite content, the wear mechanism of PI composites is translated from adhesive wear to abrasive wear.