Unidirectional liquid crystal (LC) alignment by a polarized UV exposure was examined using various polyimides (PIS) which consist of different tetracarboxylic dianhydrides and diamines, The dichroic ratios and anchoring energies of the LC cells were measured as a function of polarized UV exposure time. The results suggest that the unidirectional LC alignment for UV dosage is largely affected by the chemical structures of the PIS used. The LC alignment properties are summarized with respect to the UV absorption efficiencies, molecular conformations, and mechanisms of decomposition of the PI films.