Compost from vegetable residues is usually used as an organic amendment to soil; however, their thermal degradation characteristics show that it could be used as raw material in air gasification facilities. According to the obtained data, hydrogen production is positively affected by composting, increasing hydrogen concentration in the raw gas from 15.2 to 22.6 vol%. This effect is related with physicochemical changes that occur during thermophilic stage of composting. After this step it does not observes any progress on hydrogen production. On the other hand, in order to compare thermal degradation of a biomass (Leucaena leucocephala) and two composts with different maturation levels, non-isothermal thermogravimetric analysis (TGA) has been used. Under inert atmosphere, data have been adequately simulated assuming three fractions (hemicellulose, cellulose and lignin) in both biomass and composts. However, under air atmosphere we have used a simplified model that assume two components in biomass (holocellulose and lignin) and three in composts (including humic substances). Using nth-order kinetic equations to describe component degradations, we have calculated a set of kinetic parameters which do not differ of the reported for other lignocellulosic materials. This procedure allows obtaining an approximate composition of samples. (C) 2009 Elsevier Ltd. All rights reserved.