We have investigated the alignment of polyimide backbone structures induced by single oblique angle irradiation with un-polarized light (UP-light) of wavelength 340 similar to 500nm. The polyimide (Azo-PI) used in this study contains azobenzene in the backbone structure. The alignment of the backbone structure occurs through random angular rotation of the azobenzene molecule accompanied by its photoinduced trans-cis-trans isomerization. The photo-alignment treatment was performed on 16 nm thick films of polyamic acid (Azo-PAA) that is the precursor of Azo-PI. Subsequently, the Azo-PAA film was thermally imidized. The UP-light exposure was varied up to 882J/cm(2). The orientational distribution of the Azo-PI backbone structure was determined, using polarized infrared absorption spectroscopy. We found that the average inclination angle and the in-plane order parameter of the backbone structure increased with UP-light exposure, reaching 51 degrees from the surface plane and 0.1, respectively, at 882J/cm(2).