The scratch deformation behavior of neat and wollastonite-containing ethylene-propylene copolymer composites has been studied by electron microscopy and atomic force microscopy techniques. The study indicates that the severity of plastic deformation during scratch testing in reinforced ethylene-propylene copolymers is a function of debonding/detachment of wollastonite mineral particles from the ethylene-propylene matrix. The resistance to scratch deformation was evaluated in terms of scratch hardness, scratch depth, average scratch roughness, and change in gray level before and subsequent to scratching. The data suggests that resistance to scratch deformation follows the sequence: coated + coupled wollastonite-containing EP copolymer > fine wollastonite-containing EP copolymer > coated wollastonite-containing EP copolymer > coarse wollastonite-containing EP copolymer > neat EP copolymer. EP copolymer containing coated wollastonite and coupling agent is characterized by highest scratch hardness and minimum scratch depth and scratch roughness. The visibility of scratch, quantified in terms of gray level, suggests that coated + coupled wollastonite-containing copolymer exhibits significantly reduced susceptibility to stress whitening, and is characterized by a lower gray level in the scratch-deformed regions. In the present case of wollastonite-containing copolymer composites, the resistance to scratch deformation follows a trend similar to that of gray level or scratch visibility. (C) 2004 Society of Plastics Engineers.