Sum-frequency vibrational spectroscopy can be used to study photoinduced structural change at polymer Surfaces. Results on rubbed and unrubbed surfaces of poly(vinyl cinnamate) (PVCi), a well-known photopolymer, show that polarized UV irradiation dimerizes rather than isomerizes the protruding cinnamoyl side chains at the surfaces and creates significant surface structural anisotropy needed in many applications. Anchoring energy measurements of a nematic liquid crystal film on PVCi irradiated by low UV dosages yield results in good correlation with the observed spectral anisotropy.