Papilio nephelus has a wingspan reaching about 10–12 centimetres (3.9–4.7 in). The basic colour of the wings is black, with a chain of white spots on the forewing and a large white area on the hindwing. The underside and the upperside of the wings in this species are very similar. The hindwings have wavy margins, with long tails. The thorax and the abdomen are black.