Pyrolytic species of two kinds of lignites (samples A and B) are investigated in-situ with pyrolysis-vacuum ultraviolet photoionization/electron impact mass spectrometry (PVUVPI/EIMS). Mass spectra of pyrolytic fragments are measured during temperature-programmed pyrolysis process of two lignite samples and the intensity profiles of the pyrolytic species are estimated in different temperatures. Experimental results show that H-2, H2O, CO, and CO2 are dominant inorganic gaseous products and their characteristic temperatures are in accord with the temperatures of related chemical bonds cleavage. Mononuclear aromatics are dominant organic pyrolysis products, and many olefin species are also identified. The differences between samples A and B on macromolecular structures make the distribution of pyrolytic products different. In addition, the peak of H2S and CH3SH are both clearly observed in mass spectra of sample B, which could come from thioether bonds decomposition. This work also illustrates that the PVUVPI/EIMS performs very well in in-situ analysis pyrolytic products. (C) 2015 Elsevier B.V. All rights reserved.