Syllepte mesoleucalis is a moth in the Crambidae family. It was described by Hampson in 1898. It is found in South Africa. The wingspan is about 30 mm. The wings are yellowish-white, thickly irrorated and suffused with fuscous grey. The forewings have a curved black antemedial line and a sinuous postmedial line excurved from the costa to vein 3, then bent inwards to vein 2 and oblique to the inner margin. The area between the two lines is without the fuscous irroration or suffusion from the costa to vein 2. There is a pale centered discoidal stigma. The hindwings have a pale costal area and cell, from the base to the black postmedial line. This line has pale with marks on the outer side. There is a discoidal black spot.