The present invention provides: reinforcing fibers which use an adhesive component that does not contain resorcinol and formalin, and which exhibit excellent adhesion especially to a rubber adherend that has high polarity; a method for producing the reinforcing fibers; and an elastomer product which uses the reinforcing fibers.　The present invention provides reinforcing fibers, each of which has an adhesive layer that is configured from an adhesive component containing a liquid conjugated diene rubber and a crosslinking agent on at least a part of the fiber surface, and which are characterized in that the solubility parameter (SP value) of the liquid conjugated diene rubber as calculated by a Fedors method is larger than 9.0 (cal/cm3)1/2.