The Sr(B'Ta-0.5(0.5))O-3 ceramics where B' = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Er, and Yb have been prepared by the conventional solid-state ceramic route and their microwave dielectric properties have been investigated. The structure and microstructure of the ceramics have been characterized by X-ray diffraction and scanning electron microscope techniques. The relative permittiviy (epsilon(r)) varies linearly with B'-site ionic radii, except for La, and the temperature coefficient of resonant frequency (tau(f)) varies linearly with the tolerance factor. The Sr(B'Ta-0.5(0.5))O-3 ceramics have epsilon(r) in the range 25.9-32, Q(u) x f=4500-54 300 GHz, and tau(f)=-79 to -42 ppm/degrees C. A slight deviation from stoichiometry affects the dielectric properties of these double perovskites. Partial substitution of Ba for Sr could tune the dielectric properties. Addition of rutile (TiO2) lowered the sintering temperature and improved the dielectric properties of Sr(B'Ta-0.5(0.5))O-3 ceramics.