The purpose of this article is that the silicamodified SBR/BR blend replaces natural rubber (NR) in some application fields. The styrene-butadiene rubber (SBR) and cis-butadiene rubber (BR) blend was modified, in which silica filler was treated with the r-Aminopropyl-triethoxysilane (KH-550) as a coupling agent, to improve mechanical and thermal properties, and compatibilities. The optimum formula and cure condition were determined by testing the properties of SBR/BR blend. The properties of NR and the silica-modified SBR/BR blend were compared. The results show that the optimum formula was 80/20 SBR/BR, 2.5 phr dicumyl peroxide (DCP), 45 phr silica and 2.5 mL KH-550. The best cure condition was at 150 degrees C for 25 min under 10 MPa. The mechanical and thermal properties of SBR/BR blend were obviously modified, in which the silica filler treated with KH-550. The compatibility of SBR/BR blend with DCP was better than those with benzoyl peroxide (BPO) and DCP/BPO. The crosslinking bonds between modified silica and rubbers were proved by Fourier transform infrared analysis, and the compatibility of SBR and BR was proved by polarized light microscopy (PLM) analysis. The silicamodified SBR/BR blend can substitute for NR in the specific application fields. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 120: 3695-3700, 2011