Abstract: Ultra-thin freestanding polyimide(PI) films of 100 nm thickness were formed by sequential evaporation of 4,4'-diaminodiphenyl ether(ODA) and pyromellitic dianhydride(PMDA) precursor monomers followed by a thermal treatment of 150 ℃ 1 h and 350 ℃ 2 h. The chemical structures of the PI films were investigated using FTIR spectroscopy and the degree of imidization was calculated. Results show that the PI film has a fully imidization. The surface morphology of the films, compared with co-deposited PI films, was observed using AFM, the surface morphology of the PI films would be better by depositing ODA first.