The photoconduction mechanism in a metal-free phthalocyanine pigment dispersed in a polymer matrix was investigated. The charging potential started to decay remarkably after a threshold light exposure. The threshold exposure increased as the initial potential increased and as the thickness of the photoconductive layer decreased. This result may indicate that the threshold exposure depends on the quantity of charge. The temperature dependence of the threshold exposure was also investigated. The threshold exposure decreases with increasing temperature. The activation energy was estimated to be 0.049eV at an electric field of 4.5 × 10⁵V/cm. This value is almost equal to that of the photogeneration process in phthalocyanine. The photoinduced decay rate after the induction period increased and the activation energy decreased with increasing field intensity. The anticipated field dependent phenomenon was not found in these results. Therefore, we think there is a possibility that the mechanism is different from the prevalent trap theory.