Abstract: Many maero and miero paleontologic data have been obtainedfrom the Late Cretaceous units ofTurkey. Any ve rleb r at e discovery is unknown since Cretaceous peri od and especialJy under the CretaceousTertiary (C/T) Boundary until ioday. Mosasaurus hoffmanni Mantell, 1829 is thefirst Reptilia vertebratediscovery from the Uppermost Cretaceous level of Türkiye. Mosasaurus hoffmanni was one of the giganticanİmal ofmarines and oceans of ali titnes and the Cretaceous period. Right and lef i maxilla fmgments and their a dozen tooih with left jugal bone of this fossîl are animportant material of this discovety which has beenfound İn the upper sinice of Beyler Dam, near DevrekaniTown of Kastamonu City, These remalns have beenfrom the sandy limestones levels of Campanian-earlymidâle Paleocene Davutlar Formationjust below C/T Boundary in the latesî Maastricllan level. This fossîlhas beenprevîously encoımtere.d in the. United States of America, Belgilim, Nederland, Poland and Bulgaria.Mosasourus hoffmanni found in this study is the youngest mosasaur in thefossü records and, meamvhile thisis thefırstdîscovery in the Western Asia.