Flyash, a waste product of thermal power stations, generated in huge quantities, has been posing problems of disposal. Attempts have been made for its utilization as a filler in elastomers and plastics; however, it has been established that untreated flyash does not at all contribute in enhancing mechanical properties of composites. The purpose of this work was to make meaningful utilization of flyash as a filler, by treating it with a titanate coupling agent and to use it as a filler in PBR. The properties under consideration were tensile strength, modulus at 100 and 400%, Young's modulus, hardness, etc. Composites were made with varying proportion of untreated and treated flyash. A two-roll mill was used for dispersing the filler in the rubber, and a compression-molding technique was used to cure the compound in sheet form. Tensile properties were measured on a computerized UTM using an ASTM procedure. Comparison of properties of composites filled with treated and untreated flyash established that treatment of flyash imparts better reinforcing properties. Tensile strength was improved by 50%, while modulus at 400%, was improved by 400%. Similarly, Young's modulus also was improved by 209%. The Titanate-coupling agent used here has promoted adhesion between flyash and the PBR. (C) 2004 Wiley Periodicals, Inc.