Single-phase BaZrO3 and BaHfO3 polycrystalline Powders were prepared by solid-state reaction and by spray-drying methods. BaHfO3 ceramic was fabricated at 1300-degrees-C for 24 h after pre-sintering HfO2 and BaCO3 powders at 1040-degrees-C for 4 h. Homogeneous powders of BaZrO3 and BaHfO3 were also prepared by a spray-drying route. The interaction between YBa2Cu3O7-x (YBCO) and BaHfO3 and BaZrO3 was investigated in the temperature range 900-1060-degrees-C using heat-treatment cycles appropriate to composite reaction processing and melt-texturing. The results indicate that neither compound reacts significantly with YBCO at 950-degrees-C, and BaHfO3 is still unreactive up to 1000-degrees-C. Both of them are also very stable during the melting-texture process. BaHfO3 and BaZrO3 are thus very promising substrate materials and buffer layers for the deposition of thin and thick films and as container materials for bulk YBCO superconductors; BaHfO3 seems to be a more stable material than, BaZrO3.