A trim attachment structure includes a door frame, trim and a clip. The door frame has an attachment part, which is formed by a single plate, and a fitting hole. The fitting hole has a square shape in which the diagonals thereof are aligned with specific directions. The trim has a pair of ribs which extend towards the inner side in the width direction of the vehicle, respectively facing a pair of end parts of the fitting hole. The clip is installed in the fitting hole. The clip includes a head part, a tube part and a latching hook. The tube part has a tip end part which projects from the fitting hole to the outer side of the attachment part in the width direction of the vehicle. Angled parts of the tip end part are held between the ribs. The latching hook is latched at the peripheral edge of the fitting hole on the outer side of the attachment part in the width direction of the vehicle.