A similar to 50 nm thick alumina layer was deposited on an Ni-based superalloy substrate by a sol-gel method. alpha-AlOOH particles presented in the layer after drying at 140 degrees C transformed mostly to alpha-Al2O3 grains within similar to 1 min at 1100 degrees C under a low oxygen partial pressure annealing environment. During the same time period, the alpha-Al2O3 grains grew significantly in the lateral direction, resulting in the aspect ratio of grain diameter to thickness of similar to 20. The presence of a preferred orientation in the alpha-Al2O3 layer suggested that the mechanism for the lateral growth was abnormal. The lateral growth mechanism appeared to become very slow when a critical thickness (similar to 100 nm) was reached.