(1-x)Pb(Mg1/3Nb2/3)O3-xLa(Mg1/2Ti1/2)O3 dielectrics were prepared by a solid-state reaction process and the structures were evaluated together with the dielectric characterization. The pyrochlore-free dielectrics were obtained with increasing La(Mg1/2Ti1/2)O3 content due to the increased electrone gativity difference. The 1/2 (111) superlattice reflection showed 1:1 ordering on the B site in all compositions. Antiphase tilting of oxygen octahedra and B-site cation displacing appeared at x50.9. Low loss (tand; 1024) dielectrics with high dielectric constant (36-900) Were obtained in the present system, and the good microwave dielectric properties were achieved in the compositions with x>0.7. The best combination of microwave dielectric properties was obtained for x50.9: e534, Qf521 280GHz, and t f5260 ppm/℃.