Objective Ordovician Kukersite oil shale is composed almost exclusively of Gloeocapsomorpha prisca （G. prisca） alginite. It is an important source rock from the Paleozoic， but it has only sporadically been detected and reported in the Tarim Basin in China. Therefore， rapid identification of G. prisca in source rocks is important geochemical work. Methods Here， kerogen from Estonian oil shale was analyzed using sequential stepwise pyrolysis at 50 °C intervals from 310 °C to 610 °C to investigate its chemical constitutions. Results We found that the pyrolyzed hydrocarbons formed by sequential stepwise pyrolysis were dominated by 5-n-alkyl-1，3-benzenediols. This probably reflects the major contribution of selectively preserved， highly resistant biomacromolecules from the outer cell walls of G. prisca. The kerogen was also characterized by a high content of short-chain alkanes， but abnormally high-carbon-number （>nC₂₉） n-alkane/enes appeared at 560 °C. A consistent formation of alkyl benzenes， alkyl thiophenes， and alkyl ketones also appeared at the middle to high temperature points （460 °C-560 °C）. All pyrolyzates had a lower carbon number and alkyl side chains with a distinct distribution of weak odd-over-even carbon numbers. The abundant and continuous generation of 5-n-alkyl-1，3-benzenediols and its homologues in the pyrolyzates can help to quickly identify whether source rocks contain G. Prisca. In addition， the composition characteristics， product changes， and product correlation of the pyrolyzates at different temperatures are helpful when investigating the structure of kerogen. The results of sequential stepwise pyrolysis suggested that the macromolecules of kerogen were formed mainly by the polymerization of 5-n-alkyl-1，3-benzenediols in G. prisca. The units in polymer macromolecules—including phenol rings， thiophene rings， and normal alkyl chains—are inter-molecularly connected by C-C and C-O bonds. Conclusions The distribution changes of different series of compounds obtained at different temperatures by sequential stepwise pyrolysis can be applied to other organic-rich oil shales. This approach can be used to reveal the details of algal evolution and determine the various sources of organic matter in kerogen.