Decatopseustis xanthastis is a moth of the family Gelechiidae. It was described by Oswald Bertram Lower in 1896. It is found in Australia, where it has been recorded from Queensland.[1]
The wingspan is about 10 mm. The forewings are bright yellow, with dark fuscous-purple markings and a broad straight fascia close to the base, with the edges concave. There is a broader straight-edged transverse fascia from three-fourths to just before the anal angle and a moderate hindmarginal band not quite reaching the anal angle, but nearly touching the second fascia at the lower extremity. The hindwings are dark fuscous.[2]