Tangvayosaurus (meaning 'Tang Vay lizard') is a genus of sauropod dinosaur from the Aptian-Albian age Lower Cretaceous Grès Supérior Formation of Savannakhet, Laos. It was a basal titanosaur, about 50 feet long, and is known from the remains of two or three individuals.
It is based on TV4-1 to TV4-36, consisting of a partial pelvis, several back vertebrae and a tail vertebra, ribs, and an upper arm bone (humerus). Another skeleton includes 38 tail vertebrae, a neck vertebra, and most of a hind limb. The type species, Tangvayosaurus hoffeti, was described by a group of a dozen scientists led by Ronan Allain in 1999. Allain et al. also referred the old species "Titanosaurus" falloti, from the same formation and based on partial thigh bones and tail vertebrae, to their genus as T. sp. The most recent review tentatively retains the genus because it is different from the only other established sauropod from the same approximate time and area (Phuwiangosaurus), but disagree with adding T. falloti to it.