The surface structures of polyamic acid and polyimide films made by vapor deposition polymerization (VDP) technique were investigated using infrared-visible sum-frequency generation (SFG). From the SFG spectra of VDP-made polyamic acid films, the polymer chains have a broad orientational distribution, and residual monomers are observed even for a sample that was kept in air for more than 3 months. The amidization reaction of surface residual monomers is quite slow at room temperature, and the reaction proceeds preferentially in the bulk film. In the early stage of curing, surface species become parallel to the surface plane. After the surface reorientation, the imidization reaction proceeds.