Effect of rubber/filler interactions on the stress-strain behavior for silica filled styrene-butadiene rubber (SBR) vulcanizates were studied in relation to the chain scissions of rubber molecules during deformation. The rubber/filler interactions were controlled by the modification of silica surface using several kinds of silane coupling agents. Information on the chain scission was obtained by the electron spin resonance (ESR) measurements. The combination of ESR results and stress-strain data revealed that, at a given strain, the tensile stress increased with increasing the interfacial interactions between rubber molecules and silica surface, and simultaneously the chain scission became remarkable. Further, the degree of chain scission was closely related to the mechanical energy applied to the vulcanizates. The cyclic tests of stress-strain measurements suggested that the chain scissions contributed to the Mullins effect. (C) 2004 Elsevier Ltd. All rights reserved.