MR fluid consists of magnetic particles and non-magnetic medium. Especially, magnetic particles should have high magnetic saturation value and low density. In that respect, Sendust is suitable magnetic particle to MR fluid. Sendust is complex compoun consist of 83.9% Fe, 9.6% Si and 6.5% Al. Flake type of Sendust has two features. One is high magnetic saturation value which guarantees high static and dynamic stress values. The other is high aspect ratio which is expected to improve sedimentation stability. And to lower the density of Sendust, we coated Sendust surface with polystyrene.