To provide a color diffusion transfer film unit which ensures high maximum density, low fog and rapid diffusion transfer.

The diffusion transfer film unit is obtained by disposing a photosensitive sheet having on a transparent support an image receiving layer, a white reflective layer, a light shielding layer and a silver halide emulsion layer combined with a dye image forming material, a transparent cover sheet having on a support a neutralization layer and a neutralization timing layer, and a carbon-black-containing alkali processing composition spread between the photosensitive sheet and the transparent cover sheet so that exposure is performed through the transparent cover sheet, wherein at least one compound selected from the compounds represented by formula (I) and at least one compound selected from the compound group represented by formulae (II-1)-(II-4) are contained in the alkali processing composition.