The Kopet-Dagh Basin is located in northeastern Iran and southern Turkmenistan. The Aitamir Formation (Albian-Cenomanian) is deposited in this basin. Based on four measured stratigraphic sections, depositional environments and relative sea level changes of the Aitamir Formation have been interpreted. Petrographic studies and field observations led to identification of carbonates and siliciclastic (mudstone and sandstone) lithofacies. Carbonate rocks are deposited in semi-restricted lagoon, lower shoreface and open marine sub-environments, while the siliciclastics are deposited in lagoon, bars, shoreface and open marine condition. Sequence stratigraphic analysis led to identification of two (Sheikh Section) and three depositional sequences (Sorkhozoo section) in the west and three (Gadganloo section) and four (Passkooh section) depositional sequences in the east parts of the study area. Comparison of interpreted sea-level curve of Albian-Cenomanian time in the Kopet-Dagh Basin with the global sea-level curve show some similarities and differences.