Styrene-butadiene rubber (SBR) is a copolymer of styrene and butadiene, and the butadiene unit is composed of cis-1,4-, trans-1,4-, and 1,2-components. Filler-polymer interactions of each component of SBR in silica-filled SBR compounds were examined by microstructure analysis of the bound and unbound rubbers. The composition ratio of butadiene and styrene units (butadiene/styrene) of the bound rubber was higher than that of the compounded rubber. Of the butadiene units, the 1,2-component of the bound rubber was more abundant than the cis-1,4- and trans-1,4-components. The filler-polymer interaction of the butadiene unit with silica was stronger than that of the styrene unit, and the interaction of the 1,2-component was stronger as compared with the others. The butadiene-styrene ratio of the bound rubber of the compounds containing the silane coupling agent was lower than for the compounds without the silane. (C) 2004 Wiley Periodicals, Inc.