Abstract.—Most species of the genus Pliosaurus come from the Northern Hemisphere, however a growing number of new specimens are now available from the Southern Hemisphere. Here a new species of Pliosaurus is described, the second for the genus from the Southern Hemisphere, collected from the upper Tithonian (Jurassic) levels of the Vaca Muerta Formation, Neuquén Province. Pliosaurus almanzai n. sp. is characterized by two autapomophies: angular participating in the mandibular symphysis and occipital condyle without a notochordal pit or several, irregularly-arranged grooves. Additionally P. almanzai can be differentiated from other Pliosaurus species by the following characters: trihedral teeth; nine or more symphyseal alveoli; 15-17 post symphyseal alveoli; and parasphenoid without ventral keel. Pliosaurus almanzai n. sp. shows that Pliosaurus species with nine or more 9 symphyseal alveoli persisted until the late Tithonian, contrary to previous assumptions that only species with six symphyseal alveoli were present.