Description of Rhynchodercetis regio, sp. nov., from Upper Cretaceous (Turonian) sediments of Vallecillo, State of Nuevo León, northeastern Mexico is based on three specimens. Rhynchodercetis regio differs from the other species of Rhynchodercetis in the exclusive combination of characters that includes the proportions of the head with its standard length, the length of the preorbital area, and the presence of an interopercle and a short mandibule. The occurrence of this fish in Mexico expands the known distribution of Rhynchodercetis in North America during the Late Cretaceous, from the Canadian portion of the Interior Sea to Mexico, in the western Tethys area.