A new wasp of uncertain affinities within the family Diapriidae is described after a single specimen preserved in mid-Cretaceous (Early Cenomanian) amber from France. The possible relationships of the new fossil within the family and related groups are discussed. The fossil was studied using phase contrast X-ray synchrotron imaging, a powerful tool recently used in palaeontology studies. Several other organisms (arthropods, plants remains and microorganisms as well) were also found in the same piece of amber, notably aquatic organisms, which supply informations on the habitat of this specimen.