► Proximate, ultimate analysis and HHV database was developed. ► Used data was specific for Spanish biomass fuels. ► Ash content reach values over 30%, higher than expected in bibliography. ► Nitrogen and sulphur quantities appear in acceptable values. Energy plays an important role in the world’s present and future. The best way to absorb the huge increase in energy demands is through diversification. In this context biomass appears as an attractive source for a number of environmental, economical, political and social reasons. There are several techniques used to obtain energy from biomass. Among these techniques, the most commonly used throughout the world is a thermo–chemical process to obtain heat. To optimize the combustion process in adequate reactors, a comprehensive study of the characterization of biomass fuel properties is needed, which includes proximate analysis (determination of moisture, ash, volatile and fixed carbon content), ultimate analysis (C, H, N, S and O composition) and calorimetry, focusing on biomass fuels obtained in Spain.