This contribution deals with the preparation and characterization of bismuth-doped yttrium iron garnets with composition BiY2Fe5O12 (Bi:YIG). The samples have been prepared by sintering of metal oxides homogenized in acetone for 10 minutes. The estimated average crystallite size of the single phase Bi:YIG synthesized at temperature 950 °C for 15 hours is ~ 65 nm. The real content of Bi3+ cations in samples was quantitatively evaluated by application of real-coded genetic algorithm to the powder X-ray diffraction patterns.