A molded product assembly includes a molded product being mountable to a body to be mounted having a mounting hole via a fastener. The molded product has a post projecting toward the mounting hole and disposed on a back surface of the molded product, at least a part of the post projecting through the mounting hole to a back surface side of the body to be mounted in mounting the molded product to the body to be mounted, and a holding portion disposed on the part of the post to hold the fastener. The fastener has a portion to be held that is held by the holding portion, and an elastic engagement leg being elastically deformable and having an engagement portion to be engaged with a peripheral edge of the mounting hole, the elastic engagement leg being located on the back surface side of the body to be mounted.