Nanopowders of Y 1−x Bi x FeO 3 (x = 0, 0.05, 0.10, 0.15) solid solutions were obtained by coprecipitation of hydroxides with simultaneous sonication and subsequent thermal treatment of the precipitate in air at 800 • C for 1 min. in the annealing-quenching mode. The results of X-ray phase analysis showed the formation of nanocrystalline solid solutions with a structure of hexagonal yttrium orthoferrite. The average crystallite size increases from 4 to 10 nm with the increasing bismuth content in the solid solution. The influence of Y 3+ substitution for Bi 3+ in yttrium orthoferrite on the photocatalytic activity of Y 1−x Bi x FeO 3 nanopowders during the Fenton-like degradation of methyl violet under the visible light irradiation has been studied. The maximum reaction rate constant of 0.0197 min −1 was shown by the YFeO 3 nanopowder, which has the smallest crystallite size of ∼4 nm. KEYWORDS coprecipitation, yttrium orthoferrite, heat treatment, nanoparticles, photocatalyst, Fenton-like reactions ACKNOWLEDGEMENTS X-ray diffraction studies and elemental analyses of samples were performed employing the equipment of the Engineering Center of the