In this study, the effect of the mineral matter of Beypazari Oil Shale on the conversion of organic carbon of oil shale into volatile hydrocarbon, polycyclic aromatic hydrocarbons (asphaltenes, preasphaltenes) and carbon in solid residue was investigated. Kerogen was isolated by successive HCl, HNO3 and HF treatments. A series of temperature-programmed pyrolysis operation was performed with raw Beypazari Oil Shale, and each product of every demineralization process. A carbon balance of the pyrolysis process was established by determination of the recovery of total organic carbon as organic products, and carbon remaining in the reactor because of the coking reactions. The removal of the material soluble in HCI washing affected the conversion of organic materials in the pyrolysis reactions. Alkali and alkaline earth metal cations affect the reactivity of oil shales and the leaching of these mineral matters with HCl caused a slightly decreases in the conversion to volatile hydrocarbons. The removal of pyrites with HNO3 did not affect the reactivity of the organic material in pyrolysis. But, removal of the material soluble in HF increased the conversion in pyrolysis reactions. It can be explained by the inhibitive effect of the silicate minerals. Complete removal of mineral matrix and isolation of kerogen increased the driving force for heat transfer since more heat was transferred from outside towards the inside of the oil shale particles, thus pyrolysis reaction might have occurred with ease and diffusion limitation might have decreased due to absence of mineral matrix. (C) 2004 Elsevier B.V. All rights reserved.