Aristolochia subgenus Siphisia comprises about 70 species, with a disjunct East- and South Asian to North- and Central American distribution. Here we describe and illustrate three new species of Aristolochia subgenus Siphisia from Vietnam: Aristolochia faviogonzalezii, A. tonkinensis, and A. tadungensis. The first two species are found in northern Vietnam while the latter occurs in southern Vietnam. Diagnostic characters distinguish the new species from their morphologically close relatives. Their distribution, ecology, phenology, ethnobotany, and conservation status are presented as well. In addition, three species are newly reported for the flora of Vietnam that were until now restricted to China, namely A. fangchi, A. hainanensis, and A. utriformis. An identification key to all Asian species of Aristolochia subgenus Siphisia is provided.