A novel non-return-to-zero (NRZ) to return-to-zero (RZ) format converter for differential phase shift keying (DPSK) signal is proposed based on phase-intensity hybrid modulation and dispersion compensation. Influence on the format conversion of the converter parameters is theoretically analyzed and format conversion of 10-Gb/s degraded DPSK signal is investigated through numerical simulation. Experimental 10-Gb/s NRZ-DPSK signal to RZ-DPSK signal conversion and the bit error rate (BER) performance of the demodulated signals have also been demonstrated. Calculation results show that low duty cycle RZ-DPSK signal with high quality can be obtained through designing the converter. Experimental results show that the power penalty of the conversion is low and the timing-jitter of the RZ-DPSK signal is lower than that of the NRZ-DPSK signal. The format converter can also be applicable to multi-wavelength and differential quadrature phase shift keying (DQPSK) operation.