Abstract In this work, a high-performance, low-complexity modulation format identification (MFI) technique is proposed and experimentally demonstrated for coherent optical receivers using features extracted from phase statistics in Stokes space. Numerical simulations as well as long-haul experiments are carried out to validate the proposed MFI scheme. Successful identification is demonstrated among polarization-multiplexed (PM) QPSK, 8PSK, 8QAM, 16QAM, 32QAM and 64QAM signals. Compared with existing modulation identification schemes, the proposed MFI method has an excellent recognition performance with a low computational complexity.