Ta-Modified lead magnesium niobate-lead titanate crystalline solutions 0.9PbMg1/3(Nb(1−x)Tax)2/3O3-0.1PbTiO3 (PMN-PT) were first synthesized. The dielectric constant and the dielectric loss of the ceramic for different compositions as a function of frequency and temperature were measured using a Hewlett Packard 4284A LCR precision meter, which can cover a frequency range from 20 to 106Hz in a Delta 9039 test chamber operated between −75°C to +330°C. Dramatic changes of the dielectric properties were observed in Ta-modified 0.9PMN-0.1PT. It was noticed that the samples with appropriate amount of Ta-doping (x = 0.1, 0.2, and 0.3) have smaller grain size, larger dielectric constant, and lower dielectric loss than those of the specimens without doping (x = 0.0) or over doping (x = 1.0) in the frequency band of 100 – 105Hz. Proper Ta-doping in PMN-PT also resulted in a weaker frequency dispersion. It was also found that with increasing of Ta addition x, the transition temperature shifts downward to the lower temperature and the peaks of the dielectric constant versus temperature are getting sharper. Ta-doped PMNTa-PT shows a typical relaxor behavior.