A new species of soldier beetle of the genus Malthodes is described from Eocene Baltic amber of the Kaliningrad region, Russia. The new species is placed within the subgenus Libertimalthodes based on the long elytra covering the last abdominal segments, the last ventrite wide and little modified, and the markedly larger aedeagus. Malthodes (Libertimalthodes) spaceae sp. nov. is the third fossil species of the subgenus Libertimalthodes and is distinguished from congeners by the last ventrite narrower and not concave in the middle of the apex or by shorter last tergite and bigger aedeagus. The recent discovery of three specimens (including M. spaceae sp. nov.) with long elytra can shed light on the origin of the genus.