Ternary single crystals xPb(In1/2Nb1/2)O3 - (1-x-y) Pb(Mg1/3Nb2/3)O3-yPbTiO3 (PIN-PMN-PT) poled along c showed remarkable electromechanical properties. We report complete sets of elastic, dielectric, and piezoelectric constants of PIN-PMN-28%PT and PIN-PMN-32%PT, measured by using combined resonance and ultrasonic methods. The electromechanical coupling coefficients k15, k32, and k33 can reach 0.95, 0.90, and 0.92, and the piezoelectric strain coefficients d15, d32, and d33 are as high as 3354 pC/N, -1781 pC/N, and 1363 pC/N, respectively. These full matrix data sets provide the base for fundamental studies on domain engineering phenomena as well as urgently needed input data for the design of electromechanical devices using  c poled PIN-PMN-PT single crystals. �� 2010 American Institute of Physics.