This study investigated the performance of magnetic fields in reducing gas back-mixing in bubbling fluidized beds with Geldart-B magnetizable particles. The Peclet number (Pe) and axial dispersion coefficient (D_a,g) were determined using the one-dimensional dispersion model. A weak magnetic field reduced gas back-mixing to a certain extent, while a moderate field resulted in minimal decrease. The performance of a strong magnetic field varied significantly depending on the operation mode. Under the magnetization-FIRST operation mode, gas back-mixing was significantly reduced. The corresponding Pe and D_a,g were calculated as ∼76 and ∼3.6 × 10⁻⁴ m²/s, indicating that the gas flow approached the ideal plug-flow manner. However, when the magnetization-LAST operation mode was used, the strong magnetic field failed to mitigate gas back-mixing. Therefore, the performance of magnetic fields in reducing gas back-mixing depended not only on their intensity but also on their application sequence to the gas flow field.