The vehicle roof antenna mounting assembly comprises a convex portion (120), a bolt (160) and a leg washer (140). The convex portion is inserted into a mounting hole (RH) of a vehicle roof panel (R) and has a edge portion (125) and a inner threaded hole (126). The bolt has a screw screwed to the threaded hole and is tightened to the convex portion. The leg washer has a plate washer ring (141), a leg portion (142) and a taper portion (144). The leg portion is extendedly provided from the washer ring toward the mounting hole. The taper portion is provided on the leg portion as opposed to the edge portion and abutted on the edge portion to expand the tip portion toward an outside of the mounting hole.