[en] In this paper, two types of polyimide (PI) fibers, namely, PI-1 and PI-2, were modified using various treatments, including silane coupling agent KH-550, SiO₂ sol–gel, and ozone treatments. The surface properties of the PI fibers and the adhesion behavior of PI fiber/epoxy composites were evaluated. The chemical compositions and surface morphologies of the PI fibers were characterized by x-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy. The results indicated that the interfacial properties of the PI fibers were enhanced after treatment with these three methods. In particular, the silane coupling agent exhibited the highest efficiency for surface modification. (paper)