The micropolydesmoid millipede family Haplodesmidae is here recorded from Cambodia for the first time through the discovery of the first, new species of the genus Eutrichodesmus Silvestri, 1910: E. cambodiensissp. nov. This new species is described from two limestone habitats in Kampot Province, based on abundant material. It is easily distinguished from all related congeners by the following combination of characters: body greyish-brown; limbus roundly lobulate; solenomere partially divided from acropodite by a digitiform lobe, but without hairpad. Brief remarks on the previously-proposed “pecularis-group” are provided and a second group, the “demangei-group”, is established and discussed on the basis of morphological evidence, updating the number of recognised species groups of Eutrichodesmus to two. Detailed morphological illustrations, photographs and a distribution map, as well as remarks on its habitat and mating behaviour of the new species are presented. Furthermore, the current distributions of all 55 presently-known species of Eutrichodesmus are provided and a key to all 23 species that occur in mainland Southeast Asia is given.