A new species, Ateuchus tona, from the eastern Andes of Colombia is described and illustrated. The unique set of characters of this species, particularly the unusual sexual dimorphism in the sixth abdominal ventrite, which is largely expanded medially only in males, clearly separates this species from all other known species of Ateuchus. The species was found in 2004 during a single sampling event in a protected area. Since in Colombia most of the cloud forests are subject to extensive deforestation, additional sampling is needed to gather information about the species' conservation status. Additionally, two species, A. parvus and A. freudei, new to Colombia are presented rising the number of the Ateuchus species known for the country to eleven.