Abstract: A molecular level characterization method for investigating composition and structure of medium and low temperature coal tar derived from Inner Mongolia lignite upgrading plant has been developed in this paper. The physi- cal and chemical properties of medium and low temperature coal tar was described from macro level. The medium and low temperature coal tar and its chemical composition under different distillation ranges and subcomponent of different natures was investigated from molecular level. Firstly,the whole fraction of medium-low temperature coal tar was sepa- rated into 16 narrow fractions by real boiling distillation,and analyzed on their properties. Secondly,the acidic frac- tion,the alkaline component and the neutral component were separated by acid-base extraction for the >180 ℃ heavy fraction,and the neutral component was separated on the extraction chromatographic apparatus to obtain six character- istic subcomponents. The compositions and molecular structures of full-range fractions,narrow fractions and sub-frac- tions were analyzed by GC / MS. Results show that the water content of all coal tar fraction is 28% ,at 20 ℃ ,the densi- ty is 1 003. 7 kg / m3 ,the oxygen content is 7. 4% ,and the fraction content (