Pre-treatment of wood is a substantially important stage to make its components more accessible for conversion to valuable products. The goal of this study was to investigate the mild hydrolysis pre-treatment of birch (Betula pendula) wood for improving the cellulosic part accessible to pyrolysis for obtaining anhydrosugars. Lignocellulose (LC) was obtained after separating hemicelluloses from birch wood chips by treating them with 3% sulphuric acid from the wood oven dry mass, followed by acid hydrolysis with steam at 100-180 ° during 60 min. Electron paramagnetic resonance (EPR) spectroscopy data showed the formation of polyconjugated systems in the LC structure, starting from a pretreatment temperature of 130 °, which, coupled with the decreasing degree of polymerisation (DP), was not favourable for the formation of levoglucosan. The optimal pre-treatment temperature can be considered to range from 120 to 130 °