We prepared a polymer liquid crystal (PLC) with ortho-substituted azobenzene to explore the effect of the structure of the photochromic unit on the formation of holographic grating. On this behavior, a remarkable difference was observed between two materials, Grating formation of the ortho-substituted azobenzene moiety proceeded faster than that of common azobenzene analogs without substituents at the ortho position. This result is explained in terms of the stability of the LC phase structure. We investigated the relationship between alignment behavior and change of the diffracted light intensity. The result shows that in the ortho-substituted azobenzene sample, the diffraction efficiency showed maximum when orientational relaxation is completed in a bright area of the interference pattern.