The dielectric properties of a ferroelectric liquid crystal mixture of low spontaneous polarizatian have been studied here as a function of D. C. bias voltage, frequency and cell thickness. A small sharp peak of dielectric constant is found to become prominent at the chiral smetic C-smectic A phase transition under the condition in which Goldstone mode is suppressed. The relaxation frequency, dielectric strength and the rotational viscosity of the Goldstone mode have been determined under D.C. bias field.