We have investigated the effect of a cleaning treatment on the orientational distribution of polyimide backbone structures in rubbed films and on the pretilt angle of liquid crystals (LCs). The rubbed polyimide films were washed in isopropyl alcohol with an ultrasonic cleaner for 5 min, and then in pure water in the same manner. The orientational distributions of the backbone structures in the unwashed and the washed polyimide films were determined by using infrared absorption spectroscopy. The orientational distribution of the polyimide backbone structures in the washed films was broader than that in the unwashed films, but the average inclination angle was the same for both films. The pretilt angle of LC was not changed by the cleaning treatment. We found that the cleaning treatment affect neither the average inclination angle of polyimide backbone structure nor the pretilt angle of LC, although it induces the relaxation of the orientational distribution of the polyimide backbone structures.