Pyrochlore samples of the Bi2-хMn0.5Cr0.5Nb2O9-Δ (х = 0; 0.35) composition were synthesized for the first time using standard ceramic method and subsequently investigated via X-ray phase analysis, impedance spectroscopy and photoelectron X-ray spectroscopy. The X-ray phase analysis data demonstrate that the sample at x = 0 is heterophase, with the main pyrochlore phase comprising an impurity phase of α-BiNbO4 (sp.gr. Pnna). Phase-pure pyrochlore Bi1.65Mn0.5Cr0.5Nb2O9-Δ, with equimolar content of manganese and chromium cations, is formed under the condition of partially vacant bismuth sublattice (sp.gr. Fd-3m:2, 10.4546(2) Å). The microstructure of the ceramics is characterized by high density and low porosity, with fused crystallites of 1–3 μm. The band gap for the direct allowed transition in phase-pure pyrochlore is 1.86 eV, while in pyrochlore with impurity this value is equal to 1.53 eV. In the case of multielement pyrochlore, 0.10 and 0.60 eV characteristic shift of Bi4f and Nb3d XPS spectra to lower energies, respectively, is observed, which corresponds to the reduced effective charge of bismuth +(3-δ) and niobium +(5-δ) cations. The XPS Mn2p spectrum of pyrochlore indicates that the manganese cations are in a mixed charge state, predominantly with +3 (Mn) effective charge. The Cr2p spectrum represents a superposition of spectra from chromium ions with +3, +4 and + 6 charge state. The electrical properties of the sample with impurity Bi1.65Mn0.5Cr0.5Nb2O9-Δ and the impurity-free sample Bi1.65Mn0.5Cr0.5Nb2O9-Δ were investigated by impedance spectroscopy. It was observed that the high-frequency dielectric constant values are higher for the sample with impurity and equal to 42, as compared to 34 (at 150 °C) for phase-pure pyrochlore. The relative dielectric constant of the samples in the 104–106 Hz frequency range is almost independent of frequency; the dielectric loss tangent is low for both samples and equal to 0.006 at 1 MHz. The activation energies of high temperature conductivity for sample with impurity and phase-pure pyrochlore are 0.82(2) and 0.44(1) eV, respectively. A significant difference in the temperature dependence of the specific electrical conductivity indicates that the presence of 20 mol% impurity is critical with respect to the reproducibility of the electrical properties of the sample. The conductivity of the sample with impurity is 1–2 orders of magnitude higher than that of the impurity-free sample. The impedance hodographs of the samples were modeled by an equivalent circuit, which parameters are given in the article.