Biomass samples were submitted to thermoanalytical investigation to evaluate their thermal behaviour in both oxidizing and inert atmospheres. The trend of the t.g.a, and d.t.g, curves in air or He were evaluated to obtain information on reactivity of the samples and some correlations with their analytical characteristics. In particular, evaluation of lignin content was found to be useful to predict biomass thermal behaviour and the quality of pyrolysis products obtained. As the standard determination of lignin content is complicated, an alternative method using thermogravimetry was also used. A simple laboratory apparatus was used to obtain the pyrolysis products of the biomass samples, allowing a small amount of oil to be collected for thermogravimetric evaluation of its quality. The quality of biomass-derived oil depended on the lignin content of the starting material. Comparison of the thermogravimetric curve of the bio-oil with the corresponding curve of a bio-oil sample produced in an industrial plant showed that the oils obtained in the laboratory apparatus were considerably lighter and therefore better suited for use as fuel.