An electrophotographic image forming apparatus and a development cartridge are provided. The electrophotographic image forming apparatus including a body including an opening, a photoreceptor cartridge attached to, or detached from, the body through the opening, and including a mounting portion, and a development cartridge attached to, or detached from, the mounting portion through the opening while the photoreceptor cartridge is mounted in the body. The mounting portion includes first and second guide rails, and both side portions of the development cartridge respectively include first and second guide protrusions having different protrusion amounts from the both side portions to be respectively guided by the first and second guide rails.