Elachista megagnathos is a moth of the Elachistidae family that is found in Russia (the Russian Far East and the southern Ural Mountains). The length of the forewings is 2.6–2.9 millimetres (0.10–0.11 in) for males. The head and thorax are shining silvery grey-brown. The forewing ground colour is blackish brown with a bronze lustre and silvery marks with goldish lustre. The hindwings are brown. Adults have been recorded in July in the Russian Far East.