We could optimize the crystallinity of azopolymers for sensitive and stable holographic recordings by controlling the ratio of crystalline unit of the main chain of azopolymers. In this study, we synthesized several azopolymers with the different ratios of crystalline and amorphous moieties of the main chain. Those polymers clearly had different crystallinity depending on the ratios. We measured their photo induced birefringence, which contributes to the formation of a hologram, and evaluated their photosensitivity defined as the growth speed of the birefringence. We also examined the relaxation properties of the induced birefringence after the recording. As a result, we found that the azopolymer of which the main chain consisted of 90% crystalline moieties and 10% amorphous moieties represented the best sensitivity performance. After irradiation, the birefringence relaxation for it was suppressed to one eighth of that for a 100% amorphous azopolymer. Furthermore, TEM image revealed that several microcrystals less than 20 nm in diameter, which caused negligible light scattering, existed in this 90% crystalline azopolymer. The microcrystal domains seemed to help the azobenzene moieties maintain the orientation, which resulted in the stabilization of the recorded birefringence. Therefore, it could be said that the microphaseseparation is the key for achieving optical recordings.