An image forming apparatus and a process cartridge having a photoreceptor including an electroconductive substrate; and a photosensitive layer located overlying the electroconductive substrate and comprising a charge generation material, a charge transport material and an inorganic filler, wherein the content of the inorganic filler at a surface side of the photosensitive layer is greater than that at a bottom side of the photosensitive layer near the electroconductive substrate, and wherein an outermost layer of the photoreceptor has a water vapor permeability not greater than 50 gm.sup.31 224 h.sup.-1.