An arrangement structure for an auxiliary component of a vehicle includes a floor panel defining the bottom surface of the passenger compartment. The floor panel includes a first kick-up portion and a second kick-up portion disposed in side-by-side relation to the first kick-up portion in a lateral direction of a vehicle body. The second kick-up portion is formed to have a height greater than that of the first kick-up portion. A first seat is disposed on the first kick-up portion, a second seat is formed to have a smaller size than that of the first seat and disposed on the second kick-up portion, and a cross member is joined along the second kick-up portion in the lateral direction to form a closed section therebetween. The arrangement structure of the present invention allows a vehicle to have a low overall-height compact body while achieving enhanced layout flexibility and assuring a passenger compartment space.