A cover screw for a dental implant seals a threaded hole of an implant fixture formed in a mandible or maxilla. The cover screw is formed of a main body and a membrane fixing screw, and is attached to the implant fixture until the implant fixture is thoroughly connected to the mandible or maxilla in an implantation hole. The main body includes a first male screw to be screwed into the threaded hole of the implant fixture, an outer face formed on a side opposite to the male screw and facing an oral cavity, and a threaded hole formed on a side of the outer face. The threaded hole has a diameter smaller than that of the male screw and extends parallel to the male screw. The membrane fixing screw has a head, and a second male screw to be screwed in the threaded hole. A barrier membrane is properly held between the main body and the head.