The measurements of magnetic susceptibility, EPR and NEXAFS- spectroscopy study of the iron-containing solid solutions of bismuth niobate Bi₃NbO₇ has indicated that iron atoms are represented by monomeric Fe(III) and Fe(III)-O-Fe(III) exchange bound dimers with the ferromagnetic and antiferromagnetic types of exchange in the solid solutions of cubic modification. The exchange parameter and monomeric and dimeric cluster distribution in Bi₃Nb_1-xFe_xO_7-δ depending on the content of the paramagnetic atoms were calculated according to the model of Heisenberg-Dirac-van Vleck. The solid solutions as well as iron oxides FeO, Fe₂O₃ and Fe₃O₄ were studied by the NEXAFS spectroscopy in order to determine the degrees of oxidation of iron atoms. The analysis of the NEXAFS Fe2p-spectra of iron-containing solid solutions and iron oxides revealed that the studied Fe atoms were mainly in the +3 oxidation state. The  EPR spectrum of the sample with minimum iron content contained a symmetric signal with g = 4.27 with a weak shoulder at g ~ 8. The samples of Bi₃Nb_1-xFe_xO_7-δ solid solutions at 0.02 ≤ х ≤ 0.04 had a low-intensity broad band in the region of g ~ 2.28 of their spectra. The spectra of  EPR of the solutions with x > 0.04 exhibited a broad, slightly asymmetric line centered around g ~ 2.0.