Abstract Nano-Fe 2 O 3 –TiO 2 composite was prepared through the gaseous detonation method. The effects of Fe 3+ contents on the morphology, properties, and photocatalysis of nano-Fe 2 O 3 –TiO 2 composite were also studied. Sample structures, components, particle size, morphology, and optical properties were characterized by X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy, UV–vis spectroscopy, and Fourier transform infrared spectroscopy. Photocatalytic activity was tested through a UV-based methyl orange solution degradation experiment. Results demonstrated that high Fe 3+ content can promote the conversion of TiO 2 from the anatase phase to the rutile phase, reduce the energy gap of samples, increase the photoresponse range, form Fe 2 O 3 –TiO 2 heterojunctions, and increase the photocatalytic activity of TiO 2 . When the Fe:Ti molar ratio of the precursor was 1%, the sample exhibited an anatase–rutile mixed crystal structure. The average particle size was approximately 20 nm, and the energy gap was 3.1 eV. The method achieved the highest photocatalysis at an apparent reaction rate constant of 0.142 min −1 .