Aristolochia laotica, a new species from Northeastern Laos, is described and illustrated here. The horseshoe-shaped perianth tube, the 3-lobed limb, and the 3-lobed gynostemium support its placement into Aristolochia subgenus Siphisia. Of the species with cylindric or saccate-shaped limb, the new species resembles A. vuquangensis. However, it differs from the latter by having an oblanceolate to narrowly elliptic leaf lamina with a truncate to shallowly cordate base, pinnate veins, sparsely brown hirsute to glabrescent perianth, uniformly purple inner surface of utricle, indistinct, straight, strongly inflated limb lobes, and pubescent and warty inner surface of the limb lobes. Detailed description, color illustrations, and remarks on ecology, conservation status are also provided, along with a key to species reported in Laos and comparison with its similar species.