The dielectric properties of a ferroelectric liquid crystal mixture of low spontaneous polarization 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 smectic 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. field.