The structural stability and microstructure of (1−x)Ba(Mg1/2W1/2)O3−xBa(RE2/3W1/3)O3 (RE = Sm, Dy, Y, Yb) ceramics have been investigated by X-ray diffraction (XRD), Raman spectrometry, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) in this work. Microwave dielectric properties were studied in the frequency range 7–13 GHz. Phase-pure solid solutions formed in space group Fm-3m within the compositional range of x = 0.01–0.05. The local ordering of the two cations (RE3+ and W6+ or Mg2+) produced an internal lattice-induced strain and charge-imbalance clusters which greatly affected the structural stability and Q × f value.