Four types of magnetorheological (MR) suspensions with four different amounts of iron oxide microfibers were prepared. Electrical devices made with these MR suspensions were introduced into a static magnetic field, being superimposed over AC field with a standard frequency of 1 kHz to measure their both equivalent electrical capacity and equivalent electrical resistance. The components of the complex dielectric permittivity obtained are influenced by the amounts of microfibers, and the relative dielectric permittivity and dielectric loss coefficient increase with magnetic field strength. The obtained effects are due to the species of iron oxides in the microfibers used in the manufacture of MR suspensions. The viscoelastic characteristics of MR suspensions were examined by steady shear flow and dynamic oscillatory tests using a rheometer under different magnetic field strengths. The Ms value of the iron micro-fibers was 22:7 Am2/kg , and the shear stress curves were fitted well using Herschel-Bulkley equation to find the yield stress, which was up to 98 Pa in a magnetic field of 257 kA/m.