Formation mechanism of β-Fe₂O₃ particles was investigated by controlling the preparation conditions such as the mixing ratio of NaFe(SO₄)₂ and Na₃Fe(SO₄)₃ to NaCl and the heat treatment temperature. The heat treatment temperature strongly affected the particle shapes and sizes. β-Fe₂O₃ was found to be formed by two different reactions; one is a solid state reaction below 490 °C, and another is a liquid phase-mediated reaction above 490 °C. β-Fe₂O₃ had granular shape with a diameter of about 50 to 100 nm below 490 °C, while at high temperatures above 490 °C cubic particles with relatively large size of about 500 nm to 2 μm were produced. We found that this dramatically change of particle morphology including their sizes and shapes was caused by the effects of the liquid phase in the reaction.