Elachista cyanea is a moth of the Elachistidae family. It is found in Australia along the eastern coast form southern Queensland to Burrewarra Point in New South Wales. The wingspan is 5.2-5.8 mm for males and 5.2-6.4 mm for females. The forewings are blue basally with black scales distally. The hindwings are dark grey. The larvae feed on Commelina cyanea. They mine the leaves of their host plant.