College of Earth Sciences，Jilin University，Changchun 130061，China

The authors study the laser Raman spectrum characteristics of organic materials in pelitic rocks in Middle Permian Zhesi Formation from Suolun area，Inner Mongolia and discuss the indication of Raman spectrum parameters on thermal evolution degree of organic materials． The spectra show an average“D1 band”peak at about 1 350. 55 cm －1 and an average“G band”peak close to 1 062. 55 cm －1 ． Distance between these two peaks is a- round 252. 00 ± ，with area ratio of“G band”to“D1 band”around 0. 52，which indicate that thermal evolution temperature of organic materials is about 250℃． The average thermal evolution temperature of organic materials es- timated by the Raman spectra geothermometer is 265℃，consistent with that estimated by the vitrinite reflectance geothermometer (273℃)． Factors that caused part of the relatively high estimated temperatures are comprehensive- ly examined． Combining the genesis mark of inorganic minerals，the authors suggest that the very low- grade meta- morphic temperature that Zhesi Formation experienced in Suolun area is likely ＜ 250℃．