An implant overdenture system is used to fix an implant overdenture onto alveolar ridge by the support of implants. The implant overdenture has artificial teeth, a denture base, and magnetic assemblies. The implants each have an implant body and a keeper. A largest circumscribed circle diameter d1 in an outer shape of a surface-to-be-attracted of the keeper is equal to or larger than φ1.8 mm, and a largest diameter d2 of the implant body is equal to or larger than φ1.2 mm and equal to or less than φ3.5 mm, and these largest diameters have a relationship expressed by d1/d2≤1.5.
