Syllepte nasonalis is a moth in the Crambidae family. It was described by Hampson in 1898. It is found in South Africa. The wingspan is about 32 mm. The forewings are yellowish-brown with a dark-edged hyaline spot in the cell, conjoined to one below. There is a quadrate spot in the end of the cell and a dark postmedial line running out to an angle on vein 5, then retracted to below the angle of the cell, with a series of hyaline spots on its outer edge. The outer area is fuscous brown. The hindwings are fuscous brown with a dark antemedial line, angled on vein 5 and with an irregular hyaline band beyond it. Both wings have a dark marginal line.