Composite magnetic photocatalyst Mn_xZn_1−xFe₂O₄/β-Bi₂O₃ was synthesized by a dip-calcination method using manganese zinc ferrite as a magnetic substrate. The effects of composite mass ratio, reaction time and calcination temperature on the degradation of Rhodamine B (RhB) under the simulated sunlight were observed with various investigations. The as-prepared Mn_xZn_1−xFe₂O₄/β-Bi₂O₃ was characterized by XRD, FTIR, VSM, UV-vis DRS and SEM. The photodegradation rate of RhB in Mn_xZn_1−xFe₂O₄/β-Bi₂O₃ was higher (99.1%) than that (83.6%) in pure β-Bi₂O₃ within 2.5 h. XRD spectra revealed that the composites presented a tetragonal type, which was similar to that of β-Bi₂O₃. FTIR spectra exhibit peaks for the absorption of both Bi–O bonds and Mn_xZn_1−xFe₂O₄. The saturation magnetization (M_s) and coercivity (H_c) of the composite photocatalyst were 7.01 A m² kg⁻¹ and 25.38 A m⁻¹, respectively. DRS analysis revealed that the optical band gap of this composite was 2.31 eV, which was lower than that of β-Bi₂O₃ (2.45 eV). Moreover, the photocatalytic activity was still maintained at 82.7% after five cycles. The magnetic property with an appropriate amount of manganese zinc ferrite inhibited the recombination of photo-produced electrons (e⁻) and holes (h⁺), and enhanced the photocatalytic property of β-Bi₂O₃.