The size reduction of wood pellets during pneumatic transport in a laboratory test rig is investigated. For the quantification of pellet breakage and attrition, the length distribution of each bulk sample is measured in combination with the gravimetrical determination of the amount of fines before and after every conveying step. In laboratory tests a variation of pipe elements (bend radii, couplings, pipe reducer or cyclone separator), air volume and product mass flows and pellet quality is investigated. Additionally, particle velocities are determined with a stereoscopic high-speed camera set. Results demonstrate the strong dependence of wood pellet degradation on operating conditions and selection of pipe components. Increasing air volume flow and, thus, higher particle velocities induce particle size reduction, whereas increasing pellet mass flow has the opposite effect, although the influence is weak. Increasing pipe length or decreasing bend radius leads to progressive formation of fines. (C) 2019 Elsevier B.V. All rights reserved.