Insituthin films of (1−x)Pb(Mg1/3Nb2/3)O3–xPbTiO3, (PMN‐PT), with compositionx=0.1, 0.3, 0.35, and 0.4, were deposited on MgO(100) substrates by pulsed laser deposition. The optimum conditions to form (100) oriented PMN‐PT perovskite phase were at substrate temperatures in the range of 535 to 575 °C with an oxygen pressure of 200 mTorr. The Mg content in PMN‐PT films was found to be essential to the formation of perovskite phase. Heterostructures of PMN‐PT/La0.5Sr0.5CoO3(LSCO) films were prepared on MgO(100) substrates to evaluate the dielectric properties of the films. The dielectric constant of PMN and PMN‐PT films ranged from 1000 to 3800 at 10 kHz measured at room temperature. The highest dielectric constant was obtained from PMN films with 99% perovskite phase. ©1995 American Institute of Physics.