Frequency (10 Hz–1 MHz) and temperature (22–80 °C) dependent dielectric constant (both real and imaginary) of a ferroelectric liquid crystal ZLI-4851 film (21 μm thickness) showing a second order SmC*-SmA phase transition around 63.2 °C have been reported. The variation of dielectric constant as a function of temperature follows the generalized Landau theoretical model. Thermal variation of the complex dielectric constant has also been measured with different bias field strengths (0–20 V) for both the SmC* and the SmA phases. Interestingly, soft mode is observed in the SmC* phase only by applying a bias field perpendicular to the helix axis. Due to the application of the bias field, the SmC* phase loses stability of the helical structure, which is considered to be responsible for the appearance of soft mode in the present ferroelectric liquid crystal system. © 2003 American Institute of Physics.