Granite powder is an inexpensive material that can reduce the overall cost of a composite if used as a filler in epoxy and acrylonitrile butadiene styrene (ABS)-toughened epoxy matrices. Epoxy and ABS-toughened epoxy resins filled with granite powder were cast into sheets. To enhance the properties of these composites, granite powder was treated with triethoxymethyl silane coupling agent. Flexural properties, compression properties, chemical resistance, and morphology of theses composites were studied. The filler used varied from 0 to 60 wt %. Composites consisting of ABS-toughened epoxy with treated granite powder were found to be superior in mechanical properties to composites with treated and untreated granite powder. Composites with 50 wt % of granite powder was found to have maximum mechanical properties in all cases. All the three composites, i.e., untreated, treated and ABS toughened composites showed good resistance toward, acids, alkalis, and solvents. Treating granite powder with silane coupling agent enhances its mechanical properties and improves the interfacial bond between granite powder and the matrix. (c) 2007 Wiley Periodicals, Inc.