The world’s consumption of acetic acid has increased from 6.7 million t in 2002 up to 7.9 million t in 2007 and continues to grow. Besides, the production technology of this product has changed dramatically. Some years ago, when the oil price was lower, acetic acid was produced from ethanol by way of fermentation. Still now 75% of commercially used acetic acid is produced from methanol by the catalytic process. Acetic acid is currently produced by 165 companies, and its major quantity is used for producing vinyl acetate monomer. In connection with the oil price increase, it can be forecasted that it will be necessary to produce acetic acid as well as other chemical products from biomass. Therefore, our studies in this direction become increasingly urgent. To develop the theoretical foundations for the new technology, it is necessary to investigate the effect of the main parameters on the wood hemicelluloses deacetylation process. In the present work, the effect of the catalyst amount on the alder wood hemicelluloses polysaccharides deacetylation process is investigated. The studies were carried out, treating the raw material in the presence of a catalyst with steam in an original pilot plant, with the main reactor’s volume 13,7 l and height 1450 mm. This pilot plant makes it possible to model an industrial process. Kinetic studies have shown that the alder wood hemicelluloses polysaccharides deacetylation reaction rate constant has decreased during the process. For example, at the temperature 430 K and the catalyst amount 1.0% from dry wood, the hemicelluloses deacetylation reaction rate constant has decreased from 2.14 • 10-2 min-1 to 1.41 • 10-2 min-1 during the process. This is explained by the fact that the acetyl groups in the hemicellulose polysaccharide macromolecule are linked variously and unevenly. The acetic acid yield from alder wood, with increasing catalyst amount from 1.0% to 2.0% from dry wood, grows from 57.0% to 80.2% from the theoretically possible one, respectively. To increase this yield still more, it is envisaged to study the effect of temperature on the hemicelluloses polysaccharides deacetylation process.