The charge generation process was studied for a single layered OPC comprising CGM pigments dispersed in the solid solution matrix of CTM in binder. This type of photoreceptor showed a unique bipolar photosensitivity. Since the major carrier in this system is the hole, the charge generation sites should be localized at the top surface of the layer when positively charged, and interface between the conductive substrate when negatively charged. Considering the difference of sensitivities by charging polarities in the actual single layer OPC, we assumed a model of photoexcitement of CGM in the bulk layer and diffusion of excited state as the phonon in the layer contributing the charge generation. By resolving the diffusion equation for free particles as well as the exciton diffusion in a crystal, we could estimate the diffusion length for this system as approximately 5μm and about 25% higher charge separating efficiencies at charge generation site of negative charging than that of positive charging. The theoretical result corresponded well to the experimental result for the relation between the sensitivities of both polarities.