We performed dielectric measurements of aqueous solutions of hydroxypropyl cellulose (HPC) with various concentrations in the temperature range between 25 degrees C and -20 degrees C. A primary relaxation process due to the motion of free water restricted by HPC molecules is observed at GHz region. The relaxation time and shape parameter of the primary process strongly depend on the concentration of HPC. The change of the dielectric relaxation parameters is interpreted by the results of the formation of a cholesteric phase structure of the HPC molecules.