Eudonia cyptastis is a moth in the Crambidae family. It was described by Meyrick in 1909. It is found in New Zealand. The wingspan is 17–20 mm. The forewings are fuscous, variably mixed or suffused with whitish. The hindwings are pale whitish-fuscous, with a faint yellowish tinge. The termen is suffused with fuscous. Adults have been recorded on wing in November.