To develop a photo-Fenton catalyst that works under mild conditions, we report the fabrication of Fe₂O₃  /  g-C₃N₄ composite via a simple two-step calcination process for the degradation of phenol under room temperature, neutral solution, and simulated sunlight. The photo-Fenton catalytic degradation constant of the Fe₂O₃  /  g-C₃N₄ composite is 7.07 and 7.62 times that of Fe₂O₃ and g-C₃N₄, respectively. The limited size of Fe₂O₃ and partial reduction of Fe^3  + in the Fe₂O₃  /  g-C₃N₄ composite promotes the production of   ·  OH radical. The Z-mechanism with efficient charge separation efficiency contributes to the enhanced photo-Fenton catalytic performance.