Elachista mundula is a moth of the Elachistidae family. It is found in South Australia, Victoria and Tasmania. The wingspan is 10–11.4 millimetres (0.39–0.45 in) for males and 7.8–10.5 millimetres (0.31–0.41 in) for females. The forewings are ochreous white and the hindwings are pale grey. The larvae feed on Gahnia sieberiana. They mine the leaves of their host plant. Young larvae mine downwards, creating a narrow initial gallery. Later, the mine gradually widens and reaches a length of 100–120 mm. Pupation takes place outside of the mine on a leaf of the host plant.