Abstract: An assembly method includes a succession of assembly steps of assembling fuselage components of the fuselage portion of the aircraft, for example the nose of the aircraft, to form a fuselage body, a mounting step of introducing, into the fuselage body thus formed, a floor module having at least a predetermined width, and which can be provided with items of equipment, and a fastening step of fastening the fuselage body to the floor module such that the floor module shapes the final shape of the fuselage body and the assembled fuselage portion is obtained, the floor module, which has at least a suitable predetermined width, making it possible, when it is incorporated into the fuselage body, to provide the fuselage body, which is slightly flexible, with its desired and definitive shape corresponding to the desired and definitive shape of the assembled fuselage portion.