Millipedes (Diplopoda) are well known for their toxic or repellent defensive secretions. As part of a larger investigation, we describe the chemical constituents of 14 species of Tasmanian millipedes in seven genera. Six species in the genus Gasterogramma were found to produce acyclic ketones, including the pungent unsaturated ketones 1, 2, and 6, and the novel (rel-3R,5S,7S)-3,5,7-trimethyl-2,8-decanedione (7b), for which the stereoconfiguration was established by stereoselective syntheses of pairs of isomers. These compounds have not been detected before in millipede defensive secretions. This report is the first on species of the suborder Dalodesmidea (Polydesmida), a dominant component of the soil and litter fauna of the temperate regions of the Southern Hemisphere.