The yield of the main product of the thermal destruction of cellulose - 1,6-anhydro-β,D-glucopyranose or levoglucosan (LG) in the fast thermolysis of hardwood increases several times, if pre-hydrolysis of wood in the presence of a sulphuric acid catalyst at the temperature 150-155°C is carried out, thereby achieving the hydrolysis of the main part of hemicelluloses. The lignocellulose (LC) obtained after washing is also the LG raw material. In the study, the chemical composition of the intermediate products formed in the technological process of preparing LC as well as the degree of polymerisation (DP) of cellulose in wood and the obtained LC are investigated. A possible correlation between DP and the LG yield is discussed. The component composition is determined, and the applicability and purification potentialities of the obtained intermediate products – prehydrolysis condensates and LC washing waters are evaluated. The pre-hydrolysis process condensate contains a considerable amount of acetic acid and furfural, namely, 4.7% and 10% from the oven dry wood mass, respectively. The obtained LC is washed with water till the pH 2.0-2.2 or the H2SO4 concentration from oven dry LC about 0.1% from its mass. 19-21% of oven dry wood organic substances, from which 78-88% are monosaccharides, are diluted in the washing waters. After the washing, the LC yield is 52-55% in terms of oven dry wood. During pre-hydrolysis, as a result of the action of sulphuric acid and elevated temperature, the DP of cellulose decreases from 1800-1900 in alder wood to 1200-1400 in LC. Comparing the LG yields from Kuerschner cellulose preparations prepared from the initial wood and LC, a considerably higher LG yield is obtained from the latter. The thermolysis with the corresponding wood and LC samples, carried out in parallel, has shown that the acid-treated material - LC has considerably higher LG yields, which, taking into account the cellulose content in LC (45-55%), actually correspond to the LG yield from the corresponding Kuerschner cellulose preparation. The use of the condensate for obtaining furfural and acetic acid is technically feasible. The applicability of the LC washing waters is still under study, although they do not present any problems in the wastewater biological treatment facilities.