The present invention relates to an apparatus for preventing an abutment from being loosened in a dental implant comprising: a fixture (10) which is fixedly installed in a jawbone (1); the abutment (20) coupled to the fixture (10) includes an upper hole (23a) having a bottom surface (24) and a lower hole (23b); and a fastening screw (40) for fixing the abutment (20) to the fixture, wherein the apparatus suppresses unfastening of the fastening screw (40) fastened to the screw part (13) of the fixture (10), thereby preventing the abutment (20) from being loosened from the fixture (10).