The work deals with the preparation and characterization of elastomer/multiwalled carbon nanotube (CNT) composites. Nitrile-butadiene-rubber (NBR), emulsion styrene-butadiene-rubber (E-SBR) with random segment distribution, and solution styrene-butadiene-rubber (S-SBR) having a blocked styrene content were used as elastomer matrix. The preparation of composites by a masterbatch process was compared to the direct melt-mixing process using two different types of multiwalled CNT. It turned out that extremely low-percolation thresholds of approximate to 0.2 and 1 wt% CNT can be reached by direct melt mixing of Nanocyl 7000 CNT with S-SBR and NBR, respectively. The effect of CNT on the vulcanization reaction was studied by application of a first-order kinetic model. It can be shown that the rate constants are decreasing with increasing CNT content especially at higher reaction temperatures and that CNT cause a decrease in activation energies. Temperature scanning stress-relaxation measurements were used to prove the reinforcing effect of the CNT, to verify the phase structure of the S-SBR, and to estimate the effect of CNT on crosslink density. POLYM. ENG. SCI., 2013. (c) 2012 Society of Plastics Engineers