SiC- and B4C-filled NBR rubber composites were prepared with various volume fractions of filler by a conventional roll-mill method. The morphological structures of the NBR-SiC and NBR-B4C composites were analyzed by scanning electron microscopy. The dependence of room-temperature volume resistivity (rho(v)) on the concentration of filler in the two systems was studied. In addition, variation in the number of current carriers (n), mobility carriers (mu), dielectric constant (epsilon), and dielectric loss factor (tan delta) on filler concentration in the two systems were investigated in detail. The applicability of composites as negative temperature coefficient (NTCR) linear thermistors was studied by the dependence of volume resistivity on temperature. The resistivity showed negative temperature dependence and changed linearly with temperature parallel. The conduction mechanism of the conductivity of the two composites was analyzed in terms of the computed activation energy and hopping energy. Change in volume resistivity as a function of frequency for the two systems was also investigated. Finally, the dependence of volume resistivity on applied pressure and possible real applications of these composites as transducers in pressure sensors were also studied. (c) 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2158-2165, 2007