Formation mechanism of nano-crystalline beta-Fe(2)O(3) particles was investigated by controlling the preparation conditions such as the mixing ratio of NaFe(SO(4))(2) to NaCl and heating treatment temperature. A single phase of beta-Fe(2)O(3) was formed regardless of the mixing ratio. The heat treatment temperature strongly affected the particle shapes and sizes. Below 490 degrees C, they had granular shape with a diameter of about 50 to 100 nm. While, above 490 degrees C, cubic particles with increased size of about 1 mu m were produced. All samples were antiferromagnetic at low temperature. The Neel temperature (T(N)) of 119 K for the large cubic particles was decreased to 113 K for the nanoparticles.