Concerns an evaluation of the reactivity of poplar wood in hydrogasification under the operating conditions specific for the Hynol process, using a thermobalance reactor. Parameters affecting gasification behaviour were investigated. Results showed that temperature and particle size strongly affect biomass conversion and gasification rates. Poplar wood conversion is proportional to the partial pressures of hydrogen and steam in the feed gas. It was found that gasification involves a rapid reaction of biomass thermal decomposition and a slow reaction of residual carbonaceous matter with the feed gas. A kinetic model was developed to quantitatively express gasification rates and biomass conversion as functions of reaction time. This model was used to correlate the thermobalance reactor experimental data.