Dielectric properties of Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals grown by a modified Bridgman method are investigated under strong, high-frequency (≫100 kHz) ac field. It is found that there is a phase transition due to the applied ac field, which may be due to the following reasons: (1) strong ac field periodically moves domains at fast speed that heats up the crystal due to the friction of domain change; and (2) phase transition happens because of the increase of the temperature. Compared with conventional heating techniques, ac field-induced phase transition is a quicker and more effective way. In addition, it is also found that continuous ac excitation can make the phase transition easier that may be due to the deaging effect caused by continuous ac excitation. Experimental results confirm the increase of d33 and the change of transmittance under strong ac field, which further verifies that phase transition indeed happens.