The Abtalkh Formation is one of the Upper Cretaceous rock units in the Koppeh-Dagh sedimentary basin which is considered to be of Campanian-Maastrichtian in age. The current study addresses age determination, Palynozonation, and Palynofacies of this formation in eastern Koppeh-Dagh Basin in northeastern Iran based on dinoflagellate cyst species. Accordingly, 65 rock samples were collected from the 923 thick formation and prepared and studied palynologically. The study yielded 28 genera and 45 species of dinoflagellate cysts which confirm the age of Santonian–Maastrichtian for the formation. Moreover, four zones, belonging to a superzone and one subzone, were differentiated based on the first and last appearance of index species. Furthermore, five palynofacies indicative of marginal to highly shelf basin environments were differentiated. Abundance of warm water dinocysts and the presence of fungal hyphae indicate dominance of a warm climate during sedimentation period of the formation. The study of organic matter preservation indicates a relatively low oxygen content and low rate of sedimentation.