We newly prepared liquid crystalline (LC) polymer brushes containing an azobenzene (Az) mesogenic moiety on a quartz or silicon substrate by surface-initiated atom transfer radical polymerization (ATRP). The grafted chain length was controlled by polymerization time and initial monomer concentration. The grafted chain film adopted a smectec LC phase and the molecular orientation of Az mesogens in the grafted chain was nearly parallel to the substrate plane. The in-plane photo-orientation behavior of LC polymer brushes was evaluated by polarized UV-vis absorption spectoscopy and grazing incidence X-ray diffraction measurements. Highly ordered in-plane photoalignment of Az meso-ens in the grafted chain was readily provided by the irradiation with linearly polarized visible light due to the effective light absorption of the Az mesogens aligned parallel to the substrate. The highest degree of in-plane orientation was generated at a temperature slightly above T, of the polymer. As a result. monodomain LC polymer films were readily obtained by the linearly polarized light irradiation.