The use of hammer mills is widespread, since the size of granular or fibrous materials can be reduced, the simplicity of the structures and the fineness of the milled product can be easily controlled. However, in these mills, the grinding activity, which is an important indicator of energy utilization efficiency, is lower than in other mills. In this study, the effects of technological (physico-mechanical properties, fineness grade, particle size distribution, etc.), mechanical (hammer annulus velocity, rotor dynamic characteristics, air flow in crusher unit etc.) and constructive (dimensions of crusher unit, hammer shape, the size of the gap between the unit walls and the hammer edges, the feeding technique of the crusher unit, the technique of unloading the product, the screen area, the impact plate etc.) have been investigated how such factors affect energy consumption in hammer mills.