We report skeletical remains of mosasaurids (marine varanoid lizards) from the Late Cretaceous of the Basque-Cantabrian Basin. The material consists of isolated teeth and vertebrae from the Campanian of the Alava Province and the Maastrichtian of the Treviño County, in the Northern part of the Iberian Peninsula. Four taxa, comprising two species of Mosasaurinae and two species of Plioplatercarpinae, are recognised. Mosasaurines include Mosasaurus lemonnieri, which is mentioned for the first time in theCCampanian, and Leiodon anceps, which is the first mention in the Maastrichtian of Western Europe. Additional remains belong to Mosasaurus sp., Leiodon sp. and Mosasaurinae indet. Plioplatecarpines are referred to as Platecarpus cf. ictericus, which corresponds to the first mention of the genus in the Maastrichtian of Europe, and Prognathodon solvayi, previously known only in the Maastrichtian of Belgium. The mosasaurian material from the Basque-Cantabrian Basin is the most complete set from the Iberian Peninsula to date reported.