Aigialosaurus is an extinct genus of mosasauroid within the family Aigialosauridae. Its fossils have been found in Europe. It contains two species, Aigialosaurus dalmaticus and Aigialosaurus bucchichi. According to recent molecular and morphological data, Aigialosaurus is the oldest known member of the lineage leading to large Cretaceous marine reptiles called mosasaurs, a group most closely related to snakes among living squamates.