A facile and effective hydrothermal process for the controllable synthesis of uniform hematite nanoparticles is presented. The structure and morphology of the products were characterized by powder X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The results showed that the products were uniform α-Fe₂O₃ truncated nanooctahedra bound by 8 highly symmetric quasi-trigonal facets corresponding to a probable Miller index of {102} and the particle size was around 800 nm. The formation mechanism of the products, the effects of the reaction temperature, concentration of reactant, the solvent and the Fe(III) counter ion on the size and morphology of the products were investigated. Through adjusting the concentration of the FeCl₃ solution, the size of the particles can be systematically tailored over a wide range from ca. 170 nm to ca. 2 μm. The magnetic properties and visible light photocatalytic properties of the as-obtained α-Fe₂O₃ products were investigated. The results showed that these α-Fe₂O₃ nanoparticles displayed ferromagnetic or weak ferromagnetic behavior at room temperature and exhibited a good photocatalytic property for rhodamine B.