The objective of this study was to elucidate primary and secondary reactions of cellulose pyrolysis, which was accomplished by comparing results from a micro-pyrolyzer coupled to a GC–MS/FID system and a 100g/hr bench scale fluidized bed reactor system. The residence time of vapors in the micro-pyrolyzer was only 15–20ms, which precluded significant secondary reactions. The fluidized bed reactor had a vapor residence time of 1–2s, which is similar to full-scale pyrolysis systems and is long enough for secondary reactions to occur. Products from the fluidized bed pyrolyzer reactor were analyzed using a combination of micro-GC, GC–MS/FID, LC–MS and IC techniques. Comparison between the products from the two reactor systems revealed that the oligomerization of leglucosan and decomposition of primary products such as 5-hydroxymethyl furfural, anhydro xylopyranose and 2-furaldehyde were the major secondary reactions occurring in the fluidized bed reactor. This study can be used to build more descriptive pyrolysis models that can predict yield of specific compounds.