We describe the new ichthyosaur taxon Mixosaurus panxianensis, sp. nov., from the Middle Triassic of Guizhou Province, China. Diagnostic characters of the new species include a short posteroventral jugal process and the absence of external contact between jugal and quadratojugal. The morphologic description of the type specimens amends the knowledge of the postorbital region and the postcranium of the Mixosauridae. The holotype of Mixosaurus maotaiensis, which is very fragmentary and has no taxonomic value at the species level, is found to be undiagnostic, and hence the lately introduced, monospecific genus name for this species needs to be abandoned. Phylogenetic analysis strongly supports the monophyly of the family Mixosauridae. Furthermore, the analysis shows a bifurcation of the family into two sister groups, suggesting the presence of two genera, Mixosaurus and Phalarodon. Mixosaurus, characterized by a relatively short and wide humerus, includes M. panxianensis sp. nov., M. cornalianus, and M. kuhnschnyderi. Synapomorphies of Phalarodon, which contains P. fraasi, P. callawayi, and P. atavus, are a narial shelf and the absence of a maxillary dental groove.