A group of complex perovskites, Ba2-xSrxEuSbO6 (where x = 0, 1 and 2) was synthesized and sintered as single-phase materials for their use as substrates for YBCO superconductor films. These compounds have a complex cubic perovskite (A(2)BB’O-6) crystal structure with lattice constant in the range 0.85-0.83 nm. The values of dielectric constant and loss factor of Ba2-xSrxEuSbO6 compounds are in the range suitable for their use as substrates for microwave applications of superconductor films. The dielectric constant decreases with increase of strontium content. No chemical reaction was observed between YBCO and Ba2-xSrxEuSbO6 ceramics even when they were mixed in composites of the form 80 vol% YBCO-20 vol% Ba2-xSrxEuSbO6 and processed under severe heat treatment. Addition of up to 20 vol% Ba2-xSrxEuSbO6 to YBCO showed no detrimental effect on superconducting properties of YBCO. The YBCO thick films developed on sintered specimens by dip coating were textured and showed (00/) orientation with T-c(0) = 92 K.