  We discuss the effects of cosmic phase transition on the spectrum of
primordial gravitational waves generated during inflation. The energy density
of the scalar condensation responsible for the phase transition may become
sizable at the epoch of phase transition, which significantly affects the
evolution of the universe. As a result, the amplitudes of the gravitational
waves at high frequency modes are suppressed. Thus the gravitational wave
spectrum can be a probe of phase transition in the early universe.
