In order to develop the photoresponsible materials for holographic memory, we report an amorphous azobenzene copolymer having large photo-induced birefringence (Delta n) and having good thermal stability. We have achieved large photo-induced Delta n value of 0.244 in the amorphous film containing azobenzene chromophore at the specific composition ratio. Any relaxation has not been observed even after turn off the writing beam. This large Delta n value is attributed to the effective molecular cooperative motion between two chromophores and highly anisotropic molecular structure. Also, the good thermal stability was originated from a rigid rod-like structure of long pi-conjugated copolymer segment. From the result, our copolymer can be applied as a new class of material for high performance holographic memory application.