Aluminum oxide particles are provided that include primary particles each having a hexahedral shape and an aspect ratio of 1 to 5. The aluminum oxide particles preferably have an average primary particle size of 0.01 to 0.6 μm. The aluminum oxide particles preferably have an alpha conversion rate of 5 to 70%. Further, the aluminum oxide particles preferably have an average secondary particle size of 0.01 to 2 μm, and the value obtained by dividing the 90% particle size of the aluminum oxide particles by the 10% particle size of the aluminum oxide particles is preferably 3 or less. The aluminum oxide particles are used, for example, as abrasive grains in the applications of polishing semiconductor device substrates, hard disk substrates, or display substrates.