The influence of mechanical activation of rice husk on the reactivity of the comprised carbohydrates was studied. A semicommercial centrifugal roller mill was used for the activation. The mechanical activation of the raw material was established to result in improvement of the reactivity owing to enlargement of the surface area and amorphization of crystalline fragments of cellulose. Optimal technological regimes of the activation were determined to prepare the reactive product from rice husk: rotor speed of 1500 RPM, feed rate of 30 kg/h. Particles of rice husk of 45–50 mm are obtained under these conditions. As a result, the yield of low-molecular carbohydrates increases by a factor of 7 upon complete enzymatic hydrolysis.