The magneto-rheological (MR) effect of magneto-rheological elastomers (MREs) depends on the degree of orientation of carbonyl iron particles, which are dispersed in the elastomeric matrix. In this study, viscosity and molecular weight of NR matrix decreased with the addition of peptizer, and resulted in an increase of MR effect because of the efficient orientation of carbonyl iron particles. Also, the optimum conditions for applying a magnetic field to orient carbonyl iron particles were defined by the input duration time of the magnetic field, rather than the number of input times. Ideal input duration time to induce the orientation of carbonyl iron particles on the elastomeric matrix was 15 minutes. In this system, the MR effect of MRE decreased significantly above 20,000 cycles of cyclic deformation because of interfacial failure between the carbonyl iron particles and the matrix. It was expected that the dynamic property of MRE would increase if the interfacial interaction between carbonyl iron particles and the matrix improved. POLYM. ENG. SCI., 55:2669-2675, 2015. (c) 2015 Society of Plastics Engineers