The nanostructures of the transfer films of polyimide (PI) composites generated when slid against various metallic counterparts including standard bearing steel, electroplated chromium coating (Cr), and stainless steel were comprehensively investigated. Moreover, the effect of h-BN and amorphous SiO₂ nanoparticles on the transfer film structures of the conventional composite filled with short carbon fibers and graphite were studied. It was identified that the composition of the counterparts and nanoparticles' structure exert important effects on transfer film formation. When the conventional composite rubs with the steel counterparts, obvious tribo-oxidation occurs and therefore retards material transfer. However, the composite shows a much improved tribological performance when slides against Cr due to formation of a carbonaceous transfer film. Both kinds of nanoparticles significantly mitigate tribo-oxidation and greatly enhance the tribological performance. Nevertheless, the two different kinds of nanoparticles lead to distinct transfer film structures. High resolution transmission electron microscopy analyses of transfer films reveal that tribo-sintering of nano-SiO₂ occurs, whereas h-BN particles are crushed and uniformly mixed with wear products. Moreover, h-BN transforms to c-BN probably owing to the high temperature and stress on the rubbing interface. This work can provide guidance for the formulation of best matching composites according to metallic counterparts.