Summary Refuse derived fuels (RDF) characterization and pyrolysis behaviour, carried out by means of thermogravimetric analysis, infrared and mass spectroscopy, are presented. Thermal degradation of RDF takes place through three main mass loss stages; the analyses of evolved gas allow us to discriminate the contributions of the different fractions (paper, LDPE, wood, rubber, etc.) to the global decomposition. Furthermore thermogravimetry (TG) was used for the determination of kinetic parameters, using the differential method. In order to set up the conditions of production of a good quality pyrolysis gas, the operating conditions of RDF in a pyrolysis reactor have been simulated. Data show that the volatile fraction grows with the temperature, together with the relative conversion, and that light volatile fraction (hydrogen, ethyne, etc.) gets richer, at the expense of superior homologous hydrocarbons.