The cryogenic transverse extensional and thickness shear properties of the (1 - x)Pb(Mg1/3Nb2/3)O-3-xPbTiO(3) (PMN-xPT) single crystal with the optimal crystallographic directions were investigated in present work. With the temperature down to 78 K, a characteristic decrease in piezoelectric strain constants (d(31), 2020-831 pC N-1 and d(15), 4114-2823 pC N-1) and compliance coefficients (s(11)(E), 95.3-50.6 X 10(-12) m(2) N-1 and S-55(E), 227-184 x 10(-12) m(2) N-1) was demonstrated. In comparison, the piezoelectric voltage constant (g(31) and g(15)) and electromechanical coupling coefficient (k(31) and k(15)) exhibits an almost temperature-independent behavior. Even at 78 K, high values of g(31) similar to 0.045 Vm N-1, g(15) similar to 0.057 Vm N-1, k(31) similar to 0.86, and k(15) similar to 0.94 can be obtained. Such superior low temperature piezoelectric performance is favorable for the cryogenic device designs and applications, especially for the hydrophones with high g(ij) needed. (C) 2010 Elsevier B.V. All rights reserved.