This letter presents the design and fabrication of an optical mixer based on SU8 polymer for the demodulation of polarization division multiplexed-quadrature phase shift keying (PDM-QPSK) signals. The mixer consists of two novel polarization beam splitters (PBSs) and two 4 × 4 multimode interference (MMI) couplers. It is the first polymer-based optical mixer incorporated with PDM functionality. The experimental results show good performances of the mixer.