To facilitate to mount the trim of a vehicle body, to reduce the number of part items, and to miniaturize and lighten a mounted part.

In an outer trim mounting structure whereby a pair of supporting parts 5a, 5b provided at intervals on the flexible outer trim 1 of a vehicle body are secured to a body-side mounting panel 3, a slot 13 and an approximately L-shaped supporting hole 11 having a support opening 15 which crosses and continues to the end of the slot 13 and which is smaller than the slot 13 are provided in a pair in each supporting part 5a, 5b or the mounting panel 3, and a column part 21 which fits into the support opening 15 and an engagement part 19 having an engagement piece part 23 provided at the end of the column part 21 and clamping the mounting panel 3 in combination with the supporting parts 5a, 5b are provided in a pair on each support part 5a, 5b or the mounting panel 3, and an enlarging part 25 permitting the movement of the supporting parts 5a, 5b about the column part 21 by increasing the interval to the mounting panel 3 is provided on the engagement piece part 23 at one side of the column part 21.