The Pesteliegh Formation (Lower Paleocene) in the Chehelkaman and Tang-e Neyzar area, located in the eastern Kopet Dagh Basin, has been studied to investigate its lithological facies, sedimentary environment, and sequence stratigraphy. In this part of the Kopet Dagh Basin, the Pesteliegh Formation mainly composed of conglomerates, sandstone, mudstone and shales. Petrographic studies and sedimentary structures of the Pesteliegh Formation led to the identification of three LITHOFACIES associations: conglomeratic (Gcm), sandy (Sl, Sr, Sh, St, Sp, Sm), mudstone (Fl, Fm), evaporitic facies, as well as five architectural elements (CH, LA, FF, CR, and CS). Petrological studies, sedimentary facies, architectural elements, and paleocurrent direction indicate deposition of these sediments in a meandering river system with a muddy and sandy bed, as well as floodplain and salina environments. Paleocurrent analysis also indicates a southeast to northwest flow direction which is consistent with sedimentological studies conducted on the studied sections. Sequence stratigraphy analysis of the Pesteliegh Formation indicates their deposition during a relative sea-level fall in the Lower Paleocene, comprising a depositional sequence and part of the subsequent sequence. Since the Pesteliegh Formation in the studied sections is located near the coastline, their sequence stratigraphy model follows the standard model and includes HST, LST, and TST facies associations.