Elachista obliquella is a moth of the Elachistidae family. It is found from Scandinavia to the Iberian Peninsula, Italy and Romania and from Ireland to Ukraine. It is also found in Russia.
The wingspan is 8–10 millimetres (0.31–0.39 in). Adults are on wing from April to July and again in August in two generations per year.
The larvae feed on Brachypodium pinnatum, Brachypodium sylvaticum, Bromopsis erecta, Bromopsis ramosa, Calamagrostis, Carex acuta, Carex hudsonii, Carex ornithopoda, Carex spicata, Carex sylvatica, Dactylis glomerata, Deschampsia cespitosa, Festuca, Hordelymus europaeus, Koeleria macrantha, Melica Milium and Poa chaixii. They mine the leaves of their host plant. The mine starts as a narrow, brown, ascending corridor. Most frass is deposited in the basal part. Later, the larva leaves this mine and starts making a new mine in another leaf. This mine is an elongated, somewhat inflated blotch which occupies nearly the entire width of the leaf. They are dull grey green with a light brown head. Larvae can be found from autumn to mid May and again in July.