In this paper the results of X-ray fluorescence and neutron activation analyses for 18 obsidian tools from the archaeo¬logical sites of Eastern Chia Sabz and Chogha Ahovan in western Iran are presented. The archaeological sites have materials dating from the Pre-pottery Neolithic and Chalcolithic to Uruk periods. The evidence supports our conclusion that most of the obsidian found on western Iranian sites came from sources located near Lake Van in southeastern Turkey. These results suggest that the trade route for obsidian originated in southeastern Anatolia and moved southward along the western slopes of the Zagros Mountains into the central Zagros region.