Potassium alum, potash alum, or potassium aluminium sulfate is a chemical compound: the double sulfate of potassium and aluminium, with chemical formula KAl(SO₄)₂. It is commonly encountered as the dodecahydrate, KAl(SO₄)₂·12H₂O.

Used in printing, fabrics, dyeing, manufacturing of paper, vegetable glue, baking powder, purifying water, clarifying sugar, as catalyst in ammonia synthesis, hardening agent in microscopy