A new family of microhymenopteran wasps is described and figured from three new species discovered in Cretaceous amber of Spain (Albian) and New Jersey (Turonian). Spathiopterygidae Engel and Ortega-Blanco, new family, is allied to the Diapriidae and Maamingidae (Proctotrupomorpha: Diaprioidea), sharing with these families putatively derived features relative to Monomachidae. The family contains three genera and three species, all new: Spathiopteryx alavarommopsis Engel and Ortega-Blanco, new genus and species, and Myamaropsis turolensis Engel and Ortega-Blanco, new genus and species, both from the Early Cretaceous (Albian) of Spain, and Spathopria sayrevillensis Engel, Ortega-Blanco, and Grimaldi, new genus and species, from the Late Cretaceous (Turonian) of New Jersey. Spathopria sayrevillensis is reconstructed using x-ray synchrotron microtomography In addition, a peculiar new genus and species, Iberopria perialla Engel, Ortega-Blanco, and Delclòs, of stem-group Diapriidae is described from Spanish amber. The distinctive features and character combinations of these taxa are discussed in connection with possible relationships to the surviving lineages of diaprioids.