Bayerite [alpha-Al(OH)(3)] was ground for 2 hand its structure change was characterized. Soft grinding reduces the grain size of bayerite, causes a lattice distortion in bayerite, and accelerates the phase transition from bayerite to the stable phases. With addition of alpha-Al(2)O(3) seeds, calcining the ground bayerite at 300 degrees C leads to the onset of the alpha-Al(2)O(3) formation. The onset temperature and the completion temperature of the transformation to alpha-Al(2)O(3) in the ground bayerite are about 800 and 150 degrees C lower than the onset temperature and the completion temperature of the transformation to alpha-Al(2)O(3) in the unground bayerite, respectively. The thermal decomposition of the ground bayerite undergoes the alpha-Al(OH)(3) --> gamma-AlOOH --> gamma-Al(2)O(3) --> alpha-Al(2)O(3) path without the formation of the theta-Al(2)O(3) transition phase. The effect of soft grinding on the structure of bayerite and the final thermal decomposition product of bayerite will be discussed. (C) 2008 Elsevier Ltd. All rights reserved.