Abstract Styrene‐butadiene rubber (SBR) and nitrile‐butadiene rubber (NBR) blends are immiscible. Fillers can be used as compatibilizers. The SBR + NBR blends reinforced with a mesoporous silica and a precipitated silica are characterized by studying their miscibility by the determination of rubber bound, their changes in heat capacity at each glass transition temperature, and their mechanical performance. NBR is preferentially located at the silica surface improving its dispersion. Larger rubber + filler as well as SBR + NBR interphases are obtained for the blends reinforced with the mesoporous silica, whose high surface area and organized porous structure allow a better polymer + filler interaction. The reinforced blends present higher strength at break than each reinforced polymer alone. The best performance is attained for blends reinforced with mesoporous silica. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers