Syllepte brunnescens is a moth in the Crambidae family. It was described by Hampson in 1912. It is found in Brazil (Rio de Janeiro), Panama and Mexico. The wingspan is about 30 mm. The forewings are pale reddish brown, with a paler inner half. There are traces of a sinuous antemedial line and there is a faint dark spot in the middle of the cell, as well as a discoidal lunule. The postmedial line is indistinct. The hindwings are pale reddish brown with whitish basal and inner areas. There is a slight dark discoidal bar and an indistinct dark medial line.