Lyonetia castaneella is a moth in the Lyonetiidae family. It is found in Russia (the southern part of Primorskii Territory) and Japan. The wingspan is 6.5–7 mm. There are two distinct forms, an aestival (summer) and autumnal form. The forewing of the aestival form is white, that of the autumnal form golden yellow. Adults are on wing from July to August in the southern part of the Primorskii Territory.