A front end module assembly structure for a vehicle, including: a first bracket plate provided on either a front end module or a side member, which is provided with a through hole and a slit extending upward therefrom; a second bracket plate provided on the other of the front end module and the side member to be mated to the first bracket plate, which has an insertion hole formed thereon at a position corresponding to the slit of the first bracket plate; and a locator piece attached to the second bracket plate. The locator piece has a portion configured to be inserted into the slit from a position inside the through hole and held in the slit, and a bottom face configured to be set on a periphery of the insertion hole when the locator piece is inserted into the insertion hole.