Amphoteric oxides react with both acids and bases to form salts and water.

Al2O3 (aluminum oxide) + 6HCl (hydrochloric acid) = 2AlCl3 (aluminum chloride) + 3H2O (water)

Al2O3 (aluminum oxide) + 2NaOH (sodium hydroxide) = 2NaAlO2 (sodium aluminate) + H2O (water)

Aluminum oxide is therefore an amphoteric oxide.