Polarization multiplexing is one of the effective methods to improve the transmission rate of fiber-optic communication system. A novel configuration polarization multiplexing differential phase shift keying (PolMUX-DPSK) format called dual-polarization differential phase shift keying (DPSK) (Dual-Pol. DPSK) is proposed and realized experimentally. It has the same bits symbol ratio with differential quaternary phase shift keying (DQPSK), but it needs a much simpler receiver. Unlike the conventional POLMUX-DPSK, no polarization control or polarization selection is required at the receiver. The polarization-multiplexed symbols are decoded by one Mach-Zehnder delay interferometer (MZDI) and electrical multilevel detection. The tolerances to noise and polarization mode dispersion (PMD) are analyzed and compared with single polarization state DPSK and DQPSK by numerical simulation. The results show that Dual-Pol. DPSK is more sensitive to the noise than DQPSK due to the smaller distance between symbols. For bit error rate (BER) at 10-3, the desired signal-to-noise radio of Dual-Pol. DPSK is 7dB higher than DQPSK. Compared with DPSK, Dual-Pol. DPSK has 5 ps higher PMD tolerance, but its PMD tolerance is lower than DQPSK.