The present invention relates to an implant abutment, and more particularly, to a two-piece implant abutment capable of preventing the loosening of the screw for same. The abutment according to the present invention includes a body member and a head member. The body member includes a gum coupling portion and a first prosthesis coupling portion. The gum coupling portion has the gums coupled thereto. Also, in order to have a prosthesis mounted thereto, the first prosthesis coupling portion is formed on the upper part of the gum coupling portion and has a first prosthesis slot formed downward from the top of the outer periphery thereof. The body member passes sideways therethrough. The head member includes a second prosthesis portion and a screw portion. In order for a prosthesis to be mounted thereto, the second prosthesis coupling portion is disposed on the upper part of the first prosthesis coupling portion, is formed so as not to cover the first prosthesis slot, and defines a second prosthesis slot from the upper part to the lower part in the outer periphery thereof. The screw portion extends from the second prosthesis coupling portion so as to pass through the body member and then be inserted in and screw-coupled to the fixture. According to the present invention, a first prosthesis slot and a second prosthesis slot are respectively formed in the outer peripheries of a first prosthesis coupling portion and second prosthesis coupling portion, respectively, and the outer diameter size of the second prosthesis coupling portion is formed such that the second prosthesis coupling portion does not cover the first prosthesis slot, so that even if external force is applied to the prosthesis, the screw-coupling between the second prosthesis coupling portion and fixture does not loosen. Also according to the present invention, because a first groove and second groove are formed in the outer peripheries of the first prosthesis coupling portion and second prosthesis coupling p
