Chitosan derivatives, Fluorinated chitosan, and N,N,N-Trimethyl chitosan iodide were synthesized as the disperse phases for the electrorheological fluid. The synthesis of these materials were confirmed by Fourier transform infrared spectroscopy (FT-lR). Chitosan derivative suspensions showed ER effect under the electric field. Especially, N,N,N-Trimethyl chitosan iodide suspension showed better electrorheological and electric properties than Fluorinated chitosan. It is due to difference in electron strength of polar groups composed derivatives. N,N,N-Trimethyl chitosan iodide suspension exhibited a linear dependence on an electric field power of 2.07.