The dielectric and elastic properties of [001](c)-oriented 0.7Pb(Mg1/3Nb2/3)O-3-0.3PbTiO(3) (PMN-0.3PT) crystal were investigated as a function of poling field at 300 and 360 K, respectively. At 300 K, the dielectric constant and elastic compliance of rhombohedral PMN-0.3PT crystal change drastically at a critical field corresponding to an electric-induced ferroelectric phase transition. At 360 K, the PMN-0.3PT crystal is tetragonal, its dielectric constant and elastic compliance change drastically at two critical fields, which indicates an intermediate phase. Furthermore, much small dielectric loss factors and mechanical loss factors are observed in mono-domain state, which indicates that losses mainly come from domain wall contributions.