In this study, bismuth iron oxide nanostructures were synthesized using a sonochemical method, and the effects of the hydroxide ion source (hydrazine) and low synthesis/calcination temperatures on the physical properties and photocatalytic activity were investigated. X-ray diffraction (XRD) results indicated that the samples were initially amorphous; however, crystallinity improved with calcination at 500°C and the use of an ice bath, confirming the presence of cubic and tetragonal BiFeO3 crystalline phases in the structure. Energy-dispersive X-ray spectroscopy (EDX) confirmed the presence of the relevant elements in the structure. The photocatalytic performance of the synthesized samples was evaluated by the degradation of methylene blue (MB) dye under UVA light irradiation. The synthesized Bi25FeO40 sample achieved 99.66% dye degradation in less than 8 minutes. Therefore, the optimized synthesized sample could be a suitable candidate for the treatment of industrial wastewater containing dyes.