In order to clarify the decaying process of a large surface potential of as-deposited Alq3 films on a metal electrode by heating and photoexposure, Kelvin probe method and optical second harmonic generation (SHG) measurement were employed. The change of surface potential during heating was not in accordance with the change of SH intensity at a temperature lower than 100 °C. For heating at less than 100 °C and photoexposure, x-ray diffractions showed no change. We discussed these results from a viewpoint of the disordering of orientational polar structure of Alq3 molecules and the injection of electrons from metal electrodes. Then the following model was suggested. The potential decay process of Alq3 films on aluminum (Al) electrodes by heating was found to be due to electron injection from Al electrode into Alq3 films, which does not accompany the structural change of Alq3 films in the region of temperature lower than 100 °C, though the crystallization of Alq3 evaporated film was suggested at a temperature higher than 100 °C. On the other hand, the disordering of polar structure of Alq3 film that does not accompany the structural change was elucidated as the potential decay process by photoexposure.