Pseudidonauton vexa is a species of moth of the Limacodidae family. It is found in northern and central Vietnam and south-eastern Thailand at altitudes between 280 and 380 meters. The length of the forewings is 6–7 mm for males and about 9 mm for females. Adults have a pale brown ground colour. The forewings have a basal dark area defined by a whitish distal border. Adults have been recorded in early August and from late September to early October.