A mounting structure for mounting a frame garnish on a door window frame of a vehicle is disclosed. The door window frame includes a vertical portion extending in a generally vertical direction so as to overlap a center pillar of the vehicle. The door window frame is formed to surround a door window glass of the vehicle. The vertical portion includes a hooking hole formed in an upper part of the vertical portion and an insertion hole formed in a lower part of the vertical portion. The frame garnish includes a main portion, a hooking portion, and an insertion portion. The insertion portion is inserted into the insertion hole in the vertically downward direction, and the hooking portion is inserted into and hooked to the hooking hole.