The dielectric properties and their related microstructural characteristics in solid solutions of (1 - x)Ba(Mg1/3Nb2/3)O-3 (BMN)-xLa(Mg2/3Nb1/3)O-3 (LMN) (BLMN) were investigated by measuring the relative permittivity (epsilon(r)), Q value, and temperature coefficient of resonator frequency (tau(f)), and by observing the microstructure using transmission electron microscopy, The trend of variation of the temperature coefficient of the dielectric permittivity (tau(epsilon)) was the same for our solid solutions as that reported by Reaney st al, When the tolerance factor (t) was >1.01 in BLMN with composition x = 0 to 1,0, where the tilting of oxygen octahedra,vas not involved, the components of the microstructure included a disordered and transition phase as well 1:1 and 1:2 ordered phases. In the region where 1.01 < t < 0.96 with x = 0.2 to 0.7, the 1:1 order, the disorder, and the phase due to the antiphase tilting of oxygen octahedra were present. Finally, in the region where t ( 0.96 with x = 0.7 to 1,0, the microstructure of BLMN was the same as that of the pure LMN, including the 1:1 order and the antiphase, inphase tilting of oxygen octahedra, and the antiparallel shift of A-site cations.