<p>Main idea of the paper is to find confirmation of the mechanism of chemical substitution by isovalent ions with a large-ion radius (in this case Bi ions) in the structure of M-type hexagonal ferrite. There are two hypotheses on the distribution pattern of large-radius substituent ions in the hexaferrite structure. According to one hypothesis, the substitution should occur in B positions (by substituting Fe³⁺ ions) of AFe₁₂O₁₉. This is reasonable due to the isovalence of the Bi and Fe ions and is supported by the stoichiometry. According to the second hypothesis, the substitution should occur in A positions (Bi³⁺ can substitute for a commensurate Ba²⁺ ion). This is reasonable due to the ionic size of the Ba and Bi ions and the tolerance factor principle. BaFe_12-xBi_xO₁₉ (0.1 ≤ x ≤ 0.6, ∆= 0.1) solid solutions were produced by solid-state reactions. There are a lot of techniques used to investigate prepared samples. It was determined that the single-phase region is 0.1 ≤ x ≤ 0.5. It was shown that samples with 0.1 ≤ x ≤ 0.5 contain only one phase that can be described in the frame of P6₃/mmc. For the sample with x = 0.6, impurity phases were observed: BiFeO₃ (3.45 vol.%) and BiO₂ (1.44 vol.%). It was shown that the increase of the Bi concentration from 0.1 to 0.6 leads to a decrease in the main magnetic parameters: saturation magnetization from 53.48 to 51.45&#xa0;emu/g; remnant magnetization from 27.91 to 23.71&#xa0;emu/g; and coercivity from 2.6 to 1.3 kOe. Based on concentration dependences of the main magnetic parameters, we suggest that B-site substitution is realized in BaFe_12-xBi_xO₁₉ (0.1 ≤ x ≤ 0.6, ∆= 0.1) solid solutions.</p>