The structure and dielectric properties of Bi2O3-ZnO-Nb2O5-based ceramics with pyrochlore-fluorite biphase structure were investigated. Mixed-sintered ceramics were prepared by two precalcined constituents in the system of x [Bi1.5Zn0.5 (Zn0.5Nb1.5)O7]-(1-x)Bi3/4Nb1/4O7/4 (0.05x0.35), where Bi1.5Zn0.5 (Zn0.5Nb1.5) O7 is a cubic pyrochlore (a) and Bi3/4Nb1/4O7/4 is a defect cubic fluorite (F). The phase composition of the mixed-sintered ceramics were characterized as a biphasic structure with a distorted pyrochlore (b) and a fluorite (F) coexisting. The phase ratio of b pyrochlore and F fluorite is related to the chemical composition x. The dielectric properties of the ceramics gradually change with their structure.