The inяuence of conditions of birch wood deligniёcation by hydrogen peroxide in acetic acid – water medium at atmospheric pressure in the presence of TiO2 catalyst on the yield and composition of cellulosic product was studied. It was established that the content of residual lignin in cellulosic product reduces with the increase of H2O2 and CH3COOH concentrations in the reaction medium. Simultaneously there is a decrease in cellulosic product yield.