Byasa laos, the Lao windmill, is a species of butterfly from the family Papilionidae.

The species was first described by Norman Denbigh Riley and Edward John Godfrey in 1921.

[2] The species is found in Laos and northern Thailand, of Southeast Asia region.

[3] Said to be very rare,[4] but status not known with any certainty.

[5] More data required for conservation assessment.