In situ' wide angle (WAXS) and small angle X-ray scattering (SAXS) studies were carried out to characterize the structural changes occurring during the conversion of a polyamic acid into the polyimide in the presence of fullerene, C 60 . The variations in crystallinity, long period, and the SAXS invariant of the samples are discussed in the light of the various temperature ranges studied. The conversion of the polyamic acid into the polyimide is analyzed according to the different structural steps. Results reveal that C 60 affects the degree of order of the composite in the molecular direction, giving rise to slightly smaller crystals than those found in pure polyamic acid. The difference in the SAXS data between the pure PAA and the composite are discussed through the interaction of C 60 molecules with the polyamic acid, which seems to hinder the imidization reaction up to 185 • C.