To provide a mounting structure capable of easily mounting an assist grip.

A locking piece 23 includes: an extension section 37 which extends to a rear surface side from a mounting seat body 21; and a folded section 39 which is folded from an extension end of the extension section 37, and in which a folded end constitutes a free end. A locking projection 41 is formed in a middle section of the folded section 39, and a lock member 9 has an upper side support piece part 45 which supports a folded end section 39a from an under side, in an insertion state to an opening section 25a from a surface side. In an insertion process of the locking piece 23 to an attaching hole 5 from a mounting state of the lock member 9 to a mounting seat 7 by inserting the support piece parts 45 and 46 to the opening section 25a from the surface side, the locking projection 41 comes into slide contact with a periphery edge part of the attaching hole 5, and thereby, the folded section 37 is bent downward, and passes the periphery edge part of the attaching hole 5, and thereby, the folded section 39 returns. The locking projection 41 comes into contact with the periphery edge part of the attaching hole 5 from the outside of a vehicle, and the mounting seat body 21 comes into contact with the periphery edge part of the attaching hole 5 from the inside of the vehicle.