Hydrogenation of Estonian shale oil heavy mature fraction boiling over 360 degrees C and characterized by high content of high-polar and heteroatomic compounds and by low content of aliphatic hydrocarbons was carried out in mt autoclave at various conditions to investigate the effect of temperature and time on the yield and composition of products obtained, It was found that lengthening the hydrogenation time leads to higher yields of refined oil, which is characterized by a higher content of nonaromatic hydrocarbons and as compared with oils obtained at elevated temperatures, by a higher content of undecomposed heteroatomic compounds.