A change in the particle shape as a function of the heating temperature is reported for SrO∙5.5Fe2O3 from Fe2O3 and SrCO3 in KCl (Park et al., 1996). Heating at 900ºC results in the formation of platelike particles and that at 1200ºC produces near-spherical particles. The origin of this shape change is the change in the surface structure from smooth to rough at the atomic scale. The smooth surfaces have high step energy and develop the facets, leading to the platelike shape. The various crystallographic faces on the rough surfaces have almost the same growth rate, resulting in the near-spherical shape. The rate-determining step is also changed from reaction-controlled to diffusion-controlled. The particle size is not largely dependent on the amount of salt for the reaction-controlled case, whereas the mean particle size decreases as the amount of salt is increased in the diffusion-controlled case.