The present study was devoted to the investigation of the influence of the Bi/Fe ratio in precursors on the formation of heterogeneous systems with the pyrochlore composition Bi_y+0.67δFe_yW_2-yO₆O'_δ (hereinafter BFWO)/Bi₂WO_6, and BFWO/α-Fe₂O₃ under hydrothermal conditions at 200°С in a nitric acid solution within 6 h. It was shown that at the Bi/Fe ratios of ~1–9, the two coexisting phases are bismuth tungstate (Bi₂WO₆) with the crystallite size of about 7 nm, and BFWO with the crystallite size of about 30 nm, while at the Bi/Fe ratios of ~0.05–0.33, the coexisting phases are BFWO with the crystallite size of about 40 nm, α-Fe₂O₃ and the X-ray amorphous Fe₂O₃. According to the Mössbauer spectroscopy data, the position of iron in BFWO is described by two doublets with similar chemical shifts, which indicates the inhomogeneous distribution of iron in the tungsten sublattice. The results of the local energy dispersive X-ray microanalysis (EDXMA), in combination with the data on the BFWO structure refined by the Rietveld method, as well as the TEM microstructure data, have shown the obtaining of a new pyrochlore structure, that is, BFWO, which forms within a wide range of compositions. In accordance with the refined data on the BFWO structure, it was demonstrated that this phase has the displacively disordered pyrochlore structure, in which bismuth atoms occupy the 96g Wyckoff position (WP).