The genus Thibetoides, known from the western USA and various parts of the former USSR, Turkey and Eastern Europe, is reported from Western Europe for the first time. A single female of Thibetoides aprosthemae Shaw sp. nov. was reared from a cocoon of the argid sawfly Aprosthema tardum collected in the south of France. The new species is described, figured and distinguished from its close relative T. anatolicus Kasparyan, known from S. E. Turkey. A figure is given of the very differently coloured T. acerbus Viktorov, which occurs in Ukraine and Bulgaria and is geographically the closest to the new species, and some morphological points of difference are noted.