A new fluorite-like solid solution, II-Bi1 - x Te x (O,F)2 + δ, was produced by solid-phase synthesis at 873 K with subsequent annealing, its concentration boundaries were determined, and a scheme of an isothermal (873 K) section of the BiF3-BiOF-TeO 2 system was proposed. The new phase was characterized by X-ray powder diffraction, electron microscopy, and impedance spectroscopy. Making heterovalent substitutions simultaneously in the cation and anion sublattices, Te4+ ⇒ Bi3+ and O2- ⇒ F- allowed one to vary the tellurium cation content x (at constant anion nonstoichiometry δ) or the anion nonstoichiometry δ (at constant tellurium cation content x or constant fluoride ion content), which enabled one to describe the effect of these parameters on the properties of the solid solution. The anion excess δ was found to dominate the unit cell parameter of the solid solution and its ionic conductivity. The conduction within the studied temperature range was proven to be mainly by fluoride ions. It was assumed that the ordering of superstoichiometric anions, or clustering, can manifest itself as the structural modulations of the phase II-Bi1 - x Te x (O,F)2 + δ that were detected in this work.