Abstract: Equations describing the transient response of thickness-mode piezoelectric -transducers for transmitters and receivers are derived using Laplace transform, Newton's equation and piezoelectric equation. An example of delta finction excitation is given. In conclusion it is pointed out that the pulse response is a series of ultrasonic impulses separated by a time τ=l/v when the electromechanic coupling factor k_t is neglected The influence of the medium around the piezoelectric material in the transducer upon pulse response is briefly discussed. The result suggests how to construct an acoustic matching layer so that a good transient response can be obtained.