Mechanical energy released during stirred grinding of calcium carbonate particles can promote the polymerization reactions of styrene monomers on particle surfaces, allowing us to obtain modified calcium carbonate particles by polymer grafting with less initiating reagent for reducing reaction time. This paper investigates the process of polymer grafting modification activated by mechano-chemical effects, the changes of mechanical and fluid properties of High Impact Polystyrene (HIPS) plastics with modified calcium carbonate fillers, the interactions between the modifying reagents and the surface of the filler particles and the action of the mechano-chemical effect in polymer grafting modification. (C) 2003 Elsevier B.V. All rights reserved.