The adult Asian house martin of the nominate subspecies is long, dark steel blue above with a contrasting white rump, grey-washed white underparts, and a slightly forked tail. The tail and upperwings are brownish-black, and the underwings are grey-brown. The legs and feet are brownish-pink and covered with white feathers, the eyes are brown, and the bill is black. There are few differences in appearance between the sexes, although the male is somewhat whiter below than the female, especially in fresh plumage. The juvenile bird is less glossy and has dark brown upperparts, sometimes with a brownish wash to the rump, and grey-white underparts.