Mantimalthinus balticus gen. et sp. nov. is described upon one specimen embedded in Eocene Baltic amber from the Polish coast of Gdańsk Bay. The distinctive morphological characters of the new genus are: head rounded behind the eyes, pronotum transverse with hind margin strongly bordered, elytra nearly entirely covering the last abdominal segments and metatrochanter strongly elongated. No extant or fossil genus shows these features, and only Malthinellus malickyi Wittmer, from Thailand, seems to be morphologically related to the new species.