This study was aimed to investigate the effect of mineral matter of Goynuk oil shales (GOS) on pyrolysis and product evolution. Organic part was separated from mineral matter before pyrolysis in an isothermal pyrolysis reactor. In the demineralization step, carbonate, pyrite and silicates were removed from kerogen by using HCl, HNO(3) and HF, respectively. Thereafter all samples were pyrolized in an isothermal pyrolysis apparatus. The temperatures for pyrolysis experiments were 450, 500, 550, 600, 650 degrees C. Recoveries of volatiles and total hydrocarbons increased with increasing temperature. At pyrolysis of silicate-free oil shale (GOS-F), volatile hydrocarbon recovery (VHR) increased nearly by 10 wt.% as compared with VHR from raw oil shale sample (GOS-R) at each pyrolysis temperature. Carbon content of solid residue was also calculated. The effect of mineral content of oil shale on product yield and composition was determined by establishing carbon balance in the reactor. The amount of solid residue decreased as a function of demineralization degree. The pyrolysis reaction in the presence of silicate mineral showed the catalytic effect of silicate minerals aiding coking reactions, and carbon deposition decreased averagely by 20 wt.% in silicate-free oil shale compared with the value for GOS-R at each temperature.