The growth of ruthenium (Ru) nanocrystals on the SiO2 and Al2O3 films has been investigated using atomic layer deposition (ALD) method, indicating that much higher density Ru nanocrystals are grown on the Al2O3 film compared with the SiO2 film. Ru nanocrystals with a density of 9 X 10(10) cm(-2) are obtained on the Al2O3 film in the present experiment. The typical nanocrystal height increases with ALD cycles; however, the resulting nanocrystal density decreases for long deposition time (e.g., 600 cycles) on the Al2O3 film, going with inferior size uniformity. Postdeposition annealing treatments at both 800 and 900 degrees C cause a decrease in the nanocrystal density and an increase in the medial transverse dimension of nanocrystals. Prolonged annealing time at 900 degrees C leads to a shrinkage of the medial transverse dimension of nanocrystals due to the formation of ball-like nanocrystals driven by minimizing the total surface energy. X-ray photoelectron spectroscopy analyses reveal metallic Ru nanocrystals surrounded by RuO2 which is attributed to Ru oxidation in the air.