Short-fiber-reinforced rubber composites (SFRCs) with hydrogenated acrylonitrile butadiene rubber (HNBR) as the matrix and fibrillar silicate (FS) nanofibers and short aramid microfibers (DCAFs) as the fillers were developed, and their tensile properties, compression moduli, and mechanical anisotropies were investigated. The results indicated that the properties of the HNBR/DCAF/FS composites were determined by the loadings of the FS nanofibers and DCAF microfibers. A small amount of the microfibers combined with an appropriate amount of the nanofibers resulted in synergetic reinforcement and imparted to the SFRCs significantly improved mechanical properties without substantially compromising the rubbery characteristics. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 1439-1447, 2011