Cuspilongus is an extinct genus of parasitic wasp in the sawfly family Cephidae. At the time of its description the new genus was composed of a single species named Cuspilongus cachecreekensis, known from an Eocene fossil found in North America. Subsequently, Kopylov & Rasnitsyn (2016) transferred the Early Cretaceous (Aptian) species Mesocephus ghilarovi Rasnitsyn (1988), known from the Bon-Tsagan locality in Mongolia, to the genus Cuspilongus as well.