A new group of compounds with composition (Ba5-xSrx)Nb4O15, having high permittivity and low loss have been prepared and characterised in the microwave frequency region. X-ray diffraction studies showed that monophase compound existed for all values of x from 0 to 5. Microwave dielectric properties such as epsilon(r) and tau(f) showed smooth variation with x, while the unloaded quality factor (Q(u)) showed remarkable improvement with x. A range of ceramic dielectric resonators(DR) with 40< epsilon(r) <50,-1010,000 can be obtained in this system.