We have synthesized the AB type diblock copolymer with polystyrene and poly(6-[4-(4′-methoxyphenyl)phenoxy]hexyl methacryrate) by sequential anionic living polymerization. The copolymers were prepared with quantitative yields, possessing the predictableMnvalues, compositions and narrow molecular weight distributions. The thermotropic phase behavior and structures were examined for six copolymers with the weight fraction of LC segments from 24wt% to 45wt%. All copolymers exhibit the crystal-SmA and the SmA-isotropic phase transitions. Microphase separations were examined as a function of the weight fraction of two segments and in a relation with the micro structure of LC segment.