Identification of pyrolysis intermediates and products is of great significance to better understanding of a pyrolysis process and therefore its further upgrade to practical fuels. We hereby report a real-time analysis of pyrolysis volatiles of biomass in a micro fixed-bed reactor via an on-line near-atmospheric pressure photoionization Orbitrap mass spectrometry (nAPPI Orbitrap MS). The mass spectra suggest the pyrolysis products bear a molecular weight in the range of m/z 50-300. The oxygenated compounds having between 1 and 5 oxygen atoms and with double bond equivalent (DBE) values ranging from 2 to 7 account for more than 90% of the identified peaks, indicating that significant upgrading should be developed towards applications. Pyrolysis products could be clearly distinguished from different components of biomass in the van Krevelen diagrams and DBE versus carbon number plots. The results from the nAPPI Orbitrap MS are further compared to those of off-line pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) and on-line single photoionization mass spectrometry (SPI-MS). The nAPPI Orbitrap MS is a powerful on-line approach with high sensitivity, ultrahigh-resolution, and no condensation or preparation. This analytical protocol is expected to be helpful in complicated thermochemical conversion studies, e.g. pyrolysis of biomass.