Wood powder is fine-grained biomass that can be utilised in various ways and has advantages over larger wood particles in certain applications due to smaller size and larger surface area. Present knowledge of the processing and characterisation of pulverised wood is insufficient for the efficient production and utilisation of wood powders. In this research, the effect of the operational parameters of an air classifier mill on the pulverisation process and the properties of the resulting wood powders were studied. Screened and dried Norway spruce sawdust was pulverised to very fine wood powders with median particle sizes in the range of 23 mu m-250 mu m by changing the revolution speeds of a grinding rotor and classifier wheel. Produced wood powders have various different properties, which are important in the utilisation of the powders. In the production of wood powder from dried Norway spruce sawdust with the air classifier mill, one property can be chosen independently from others, whereupon the others have certain restrictions depending on this first choice. The properties of wood powders depend on the speeds of the classifier wheel and grinding rotor and their interaction effect during processing. Average specific energy consumption depends on the speeds of the classifier and grinding rotor. An increase in the classifier speed was found to decrease the median particle size of the powder and increase the average specific energy consumption of the process. An increase in the speed of the grinding rotor was found to reduce the average specific energy consumption. (C) 2012 Elsevier Ltd. All rights reserved.