Surface hydrogenation reaction was performed in order to clarify the mechanism of photoalignment using poly(vinyl cinnamate) (PVCi). The reaction makes it possible to remove any surface ordering of the cinnamate side groups, which may happen during the photoalignment process while the generated photoproducts are still intact. After considering LC alignment and the azimuthal anchoring energy of the hydrogenated PVCi/E7 cells, it was confirmed that the alignment of liquid crystal molecules is mainly induced by the photoproducts.