Experimental results of impacts of balls on walls mimicking the collision events in grinding mills are reported. The materials for balls include steel, malachite, glass as well as a billiard ball and a cricket ball. The walls used for the impact target are steel liner, rubber liner, and slate plate. Through the measuring of translational and rotational velocities, we present the impact properties as coefficient of normal restitution, coefficient of tangential restitution and impulse ratio (or dynamic coefficient of friction). The results obtained can be used to determine explicitly the mode of behaviours (roll or slide) of the contact point during impact. They can also be used to determine parameters for discrete element method simulation. (C) 2003 Elsevier Science Ltd. All rights reserved.