Abstract: The present invention relates to an anti-loosening set screw for a carburetor, comprising a cylindrical body, a front end of the body is disposed with an adjusting section, a rear end of the body is disposed with a head with a slot, the body has a cylindrical face which is disposed with an exterior screw thread section, wherein the cylindrical face of the body is further disposed with a recessed ring groove, the ring groove is disposed with a ring-shaped elastic plastic body which is integrally formed therewith by injection molding. In comparison with the prior art, the present invention has the advantages of simple construction, close cooperation, good anti-loosening and tight sealing effects and so forth.