Amplification and simultaneous phase regeneration of differential phase-shift keying （DPSK） signals is demonstrated using a phase regenerator. Phase regeneration is achieved in a Sagnac fiber interferometer comprised of photonic crystal fiber operating in an un-depleted pump regime. The formula of signal after phase regenerator is derived. For different incident power of signal, the relations between signal-pump phase difference and signal gain are discussed, as well as the influence of fiber length on signal output intensity. The optimum parameters of the phase regenerator are given. The distributions of phase and intensities for both the non-regenerated and regenerated signals are simulated. Simulations show that nearly ideal regeneration can be achieved for the DPSK signals.