Abstract: In order to describe pyrolysis characterization of Estonia oil shale kerogen, electron paramagnetic resonance (EPR) was carried out to analyze influence of pyrolysis temperature on free radical concentration, g factors and line width (△H) of Estonia kerogen and its pyrolysates. The results show that range of free radical concentration of Estonia oil shale and its pyrolysis oil, thermal bitumen and semi-coke is between 2.29×10¹⁴ and 9.16×10¹⁴. The free radical concentration and g factor of thermal bitumen is higher than that of semi-coke. The thermal depolymerization of kerogen mainly occurs before 380℃ and intermediate thermal bitumen mainly decomposes above 380℃. The line width of the samples shows that △H of shale oil is much higher than that of semi-coke and thermal bitumen at higher pyrolysis temperature. It means that the interaction between spin particles in free radicals and the interaction between the spin particles and environment in liquids are much more severe than solid samples. Below 380℃, △H of thermal bitumen and semi-coke increases with rising temperature. The interaction between the spin particles and environment was enhanced with pyrolysis proceeding. Above 380℃, △H of thermal bitumen and semi-coke decrease, indicating that the interaction between the spin particles is weaken with the rising temperature.