Composting is biological process of decomposition of organic materials in an aerobic environment, which modifies the chemical composition and the thermal behavior of biomass. During composting, fungi and bacteria promote the decomposition of hemicellulosic Mid cellulosic fractions, increasing the lignin proportion. Its product, compost, is usually used as all amendment to soil; however, its physicochemical characteristics turn it into an interesting feedstock in pyrolysis or gasification facilities. The changes that composting produces oil biomass pyrolysis call be explained using all autocatalytic kinetic model (Prout-Tompkins). Thus, by means of a similar set of kinetic parameters for both the biomass and compost, it is possible 10 simulate the thermogravimetric analysis data (TG and DTG Curves) of the materials as a SLIM of thermal degradations of its main pseudocomponents, hemicellulose, Cellulose, lignin, and extractives. TG analysis Coupled to Mass spectrometry (MS) allows monitoring of the gas production during pyrolysis. Water and carbon oxide MS profiles call be simulated by all optimized linear combination of previously Calculated DTG curves of pseudocomponents; however, in order to simulate the hydrogen MS signal, it is necessary to consider the char obtained ill the course of the volatilization process. During pyrolysis, hydrogen production has two origins, volatilization of biomass pseudocomponents and charring, The last mechanism explains similar to 75% of the hydrogen obtained from compost. The pseudocomponent that produces more hydrogen by weight Unit is lignin, showing a specific hydrogen production much higher than carbohydrates (3:1:8 for hemicellulose/ cellulose/lignin). This fact, together with the greater lignin content ill compost, explains the positive effect of composting oil hydrogen production.