The study is aimed to determine the most perspective and effective fine-grinding mills for lignocellulosic biomass mechanical activation. Physicochemical characteristics were studied for milled crystalline cellulose and milled dry birch sawdust after their treatment in various devices – ball, planetary, ring, vortex gas driven and vortex mechanically driven mills. XRD analysis method was used for phases identification, crystallinity index (CI) and mean size of coherent-scattering region (CSR) measuring. These values are suggested to be used for an assessment of the efficiency of mechanical activation process. Mean particle size (l) of milled materials was measured with help of optic microscopy as well. As the most perspective device for future detailed investigation to be done the vortex mechanically driven mill is selected. This type of mill provides both the least electrical power consumption and activation time at adequate particles destruction level and marked mechanical activation demonstrated for dry birch saw dust (it was detected the reduction of l and CI from l ~ 3700 mm/CI =74% to l ~ 22 mm/CI = 56%).