Pb(Mg1/ 3Ta2/ 3)(0.7)Ti0.3O3 thin films of single perovskite phase were successfully synthesized by using the RF sputtering deposition technique, followed by post-thermal annealing. While the perovskite structure of Pb(Mg1/3Ta2/3)(0.7)Ti0.3O3 is rather unstable, phase evolution in the thin films was manipulated by controlling both working pressure during the sputtering process and post-thermal annealing temperature. The desirable perovskite phase was promoted by increasing the working pressure in the range of 10-25 mTorr, followed by thermal annealing at 600 degrees C. The ferroelectric, dielectric, and polarization behaviors of Pb(Mg1/ 3Ta2/ 3)(0.7)Ti0.3O3 films were characterized over a wide range of frequencies. They are strongly affected by the film thickness, where the relative permittivity and remanent polarization increase, while the coercive field decreases with increasing. lm thickness in the range of 115-360 nm.