[en] Fossil fuel consumption has increase in last few decades. This leads to many environmental problems, like global warming, the deplete ozone layer etc. The use the low-emission fuels like biomass is of growing importance. Biomass is widely available in nature. The International Energy Agency assume that heat, cold and electricity production based on biomass has the potential to provide 10% of the world’s primary energy supply by the 2035. Additionally, biofuels can replace up to 27% of world transportation fuel by 2050. Biomass can be converted into fuels via biochemical and thermochemical routes. The main thermochemical process are combustion (and co-combustion), gasification and pyrolysis. Among it, the pyrolysis has been developed as a promising method to produce liquid and gaseous fuels and char. Due to complexity of biomass structure, pyrolysis process is correlated with the chemical composition of it. Paper presents the prediction of the influence of the chemical composition of straw and wood on process pyrolysis behaviour. Cellulose, hemicellulose and lignin content of analysed biomass on possible yield of pyrolysis products was investigated.