Identification of volatile degradation products generated and released during wood mild pyrolysis is important to better understand thermodegradation mechanisms. Previous studies have shown that thermodesorption coupled to GC–MS is an attractive tool to characterize and quantify products formed during wood thermal treatment indicating higher susceptibility of hardwoods to thermodegradation compare to softwoods. The aim of this study is to elucidate wood thermodegradation pathways with special emphasis on the kinetics reactions. To achieve this objective, one hardwood species (beech) and one softwood species (Silver fir) were subjected to thermal treatment directly in the thermal desorption glass tube of thermodesorber connected to GC–MS using helium as carrier and at temperatures of 210 and 230 °C for different times ranging from 10 to 80 min. The volatiles compounds formed were analyzed by gas chromatography coupled to mass spectroscopy. From GC–MS data collected in this study, the kinetic curves of the formation of some of the products as a function of thermal treatment duration were established. Assuming that acetic acid and furfural were formed from hemicelluloses and vanillin from lignin, Arrhenius equation was used to estimate the mean activation energy formation of these two degradation by-products allowing obtaining indirect information on the thermal stability of both polymer.