The pyroelectric properties of (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) single crystals with various compositions and orientations have been investigated using a dynamic method. Excellent pyroelectric performances can be achieved in < 111 >-oriented rhombohedral PMN-xPT (0.24 <= x <= 0.30) crystals, where the measurement direction corresponds to the polar axis of the crystal. At room temperature, the pyroelectric coefficient and the detectivity figure of merit (F-d) for the < 111 >-oriented PMN-0.28PT single crystal are 8.55 x 10(-4) C.(m(2).K)(-1) and 9.89 x 10(-5) Pa-1/2 (100 Hz), respectively, superior to those of the widely used pyroelectric materials. They are also weak temperature dependent and nearly independent of frequency. These outstanding pyroelectric performances make the single crystals a promising candidate for uncooled infrared detectors and thermal imagers.