Measurements of the mean and time dependent velocity profile were obtained for the first time in an air classifier mill using particle image velocimetry (PIV). Detailed measurements in the vicinity of the impact elements and in the region of the internal classifier are presented. Different pin geometries have been studied at various circumferential velocities of the grinding disk and the classifier. Regions with high turbulence have been observed for all investigated pin geometries at the flow off side of the impact element. The classifier velocity doesn't influence the velocity profiles near the impact elements in main flow direction. The velocity profile on the front sight of the impact element, where the comminution process takes place, is constant with time and preserves a characteristic form with varying operational conditions. The one phase flow field in the complete mill geometry has been modelled by CFX.