For a photo-degradable polymeric alignment layer (CBDA-ODA polyimide), the better LC alignment is obtained by LPUV irradiation of it with 510 times less dosage than that inducing the maximum anisotropy of it. This LC alignment is improved by cleaning of the LPUV-irradiated alignment layer with water and/or IPA. It has turned out that the wet cleaning process removes the fragments or by-products formed by photo-decomposition of the polyimide and thus makes its surface more stable. This effect of the post-UV cleaning results in improvement of the LC alignment and the LC cell's properties.