The present invention provides a method for mounting an aircraft engine, which enables to speed up a mounting work by facilitating positioning of an engine with respect to a pylon. The method for mounting an aircraft engine, including: lifting up an engine of an aircraft toward a pylon that is a mounting object; and when the engine reaches a predetermined position, fixing the engine to the pylon, wherein guides that perform horizontal positioning of the engine with respect to the pylon are respectively provided on a front side and a rear side of the engine.