Oligomonoctenus neytiriae gen. et sp. nov., the second fossil representative of the family Diprionidae from the uppermost Oligocene of Aix-en-Provence, France, is described on the basis of a well-preserved compression fossil. It is compared to the other extant and fossil diprionid genera. Its morphology and wing venation support placement in the subfamily Monocteninae. Paleomonoctenus patriciae, the other diprionid described from the same paleolake, also belongs to the Monocteninae. On the other hand, the Eocene-Lower Oligocene genus Eodiprion would be attributable to the Diprioninae but needs revision. This discovery suggests that the two diprionid subfamilies were already present and diversified during the Eocene-Oligocene.