The new extinct ant genus and species, Boltonidris mirabilis, are described from the late Eocene Rovno Amber (Ukraine). This genus belongs to the tribe Stenammini of the subfamily Myrmicinae. It possesses the plesiomorphic characters of the tribe Stenammini, e.g. 12-segmented antennae with 3-segmented apical club, characteristic structure of the clypeus and frontal lobes, absence of gastral shoulder, but it has a series of autapomorphies, e.g. modified mandibles with the only two teeth on the masticatory margin, well developed longitudinal medial groove on the head dorsum, somewhat depressed areas lateral to the frontal carinae (like “vestigial” antennal scrobes), and finely swollen postero-lateral area of head, close to the occipital corners. Additionally, it has two short blunt teeth on the pronotum.