Fe₃O₄ nanoparticles grown on porous carbon are prepared as an oxygen reduction reaction (ORR) catalyst in direct methanol fuel cells (DMFCs) in which a polymer fiber membrane (PFM) is used to replace Nafion membrane. The catalyst has shown good ORR activity and high stability in alkaline methanol solution. A flexible hydrophobic cathode structure is introduced in the full cell test, the peak power density reaching 71.24 mW cm⁻² at 25 °C and 166.87 mW cm⁻² at 65 °C, respectively. This improvement is due to the combination effect of the advantages of the PFM structure and the good ORR activity and stability of the catalyst.