Altappeh (a.k.a. Ali Teppeh) is one of four major excavated caves on the southeastern margin of the Caspian Sea (the other three caves include Hotu, Kamarband, and Komishan). The site was excavated in 1963 and 1964 by Charles McBurney, and the material was given to the MMA at the University of Cambridge, the British Museum, and the National Museum of Iran. The chipped stone assemblage of Altappeh in the National Museum of Iran include 19,139 items, and based on the typological, technological, and statistical study of this collection, it seems that it might represents an older stage in the Caspian Mesolithic (compared to the other three caves), which is characterized by the use of high-quality local raw material, the production of microblades from prismatic cores, the beginning of the use of pressure technique in the production of microblades, as well as the continuation of the production of flake tools (notched or/and denticulated tools, scrapers), and the abundance of backed pieces. The technological and typological features of this assemblage (including the few number of twisted microblades, the scarcity of carinated cores, the abundance of backed blades, the beginning of geometric microliths in the form of truncated-and-backed triangulars) are most closely related to the Upper Paleolithic and Mesolithic of Western Central Asia, which is reflected in the industries obtained from the sites of Uzbekistan (the UP Kulbulakian industry and the Mesolithic Tutkaul). The typical geometric triangular microliths of Altappeh and the pressure technique has not been reported from other Mesolithic sites near it in Mazandaran. In terms of chronology, the old absolute chronologies by McBurney have to be revised or redone in order to clarify the development of site’s technological and typological features based on the periodization of the settlement stages in the cave and its relationship with the surrounding industries.