THE EFFECT of three types of carbon blacks namely: High abrasion furnace black (HAF), graphite and acetylenic carbon black on the electrical and mechanical properties of NBR composites were investigated. The conductivity of NBR composites is found to be 7 orders of magnitude higher than that of the filler-free NBR. It reaches ~10⁻³ S cm⁻¹ at ~30^oC in case of NBR composites loaded with acetylenic carbon black. The tensile strength of NBR/filler composites has been markedly increased, indicating high reinforcement efficiency, i.e., good interaction between the fillers and NBR. The NBR/HAF composites have the highest tensile strength, then NBR/Acetylenic CB and then NBR/graphite composites. The elongation at break of NBR/ filler composites was found to decrease with increasing the filler content.