A new fossil species of the genus Archaeromma Yoshimoto, 1975 was discovered in Iwaki amber from the Tamayama Formation (Late Cretaceous Coniacian) in Iwaki City, Fukushima Prefecture, Japan. The genus Archaeromma belongs to the family Mymarommatidae, and the members are called false fairy wasps because of their small bodies; only 10 species have been described from Cretaceous amber (Albian to Campanian). In this paper, we have described the new fossil species as Archaeromma chisatoi sp. nov. To the best of our knowledge, this is the second report of a fossil of the genus Archaeromma from Japan; the first one was found in Kuji amber, Iwate Prefecture. However, this is the first report of a fossil species from the Coniacian age and the first paleontological description from Iwaki amber.