Metal oxides are usually basic oxides, while those oxides of non-metals are acidic oxides. Amphoteric oxides are those oxides which show both acidic as well as basic behavior to form salts and water. Aluminium oxide reacts in this manner with acids and bases.
Al2O3 + 6 HCl ? 2 AlCl3 + 3 H2O
(Acting as a base) Acid Salt Water
Al2O3 + 2 NaOH ? 2 NaAlO2 + H2O
(Acting as an acid) Base Salt Water