A wood residue - sawdust of the mechanical processing of aspen wood - was used to obtain a short fibre filler in the form of the modified microparticles <250mkm for polymeric composite materials. To reduce energy input for wood size reduction and activation of the lignocellulosic matrix for modification, low temperature acid hydrolysis oe the residue under mild conditions was carried out. The effect of the pre-treatment parameters on thefractional and chemical composition as well as on the zeta potential and contact angle of the obtained filler was studiend. A comparison of the mechanical properties of the composites filled with initial sawdust and hydrolysed microparticles modified with a non-stoichiometric polyelectrolyte complex showed a pronounced improvement of the mechanicalproperties of the composites filled with modified wood microparticles.