The effect of potassium sulfate (K(2)SO(4)) on the phase transformation from bayerite [alpha-Al(OH)(3)] to alpha-Al(2)O(3) has been studied. K(2)SO(4) and gamma-Al(2)O(3) react and form K(3)Al(SO(4))(3). Decomposition of K(3)Al(SO(4))(3) can supply the alpha-Al(2)O(3) seeds for heterogeneous nucleation, accelerate the transformation from the gamma-Al(2)O(3) to alpha-Al(2)O(3), and lower the formation temperature of alpha-Al(2)O(3). alpha-Al(2)O(3) particles grow into hexagonal platelets in the presence of the liquid phase K(3)Al(SO(4))(3). The alpha-Al(2)O(3) platelets obtained by a 900 degrees C calcination of the bayerite and K(2)SO(4) mixture have an average diameter of 1 mu m and an average diameter/thickness ratio of 10.