Aluminium sulfate, alternatively spelt aluminum sulfate, aluminium sulphate, or aluminum sulphate; is a chemical compound with the formula Al₂(SO₄)₃. Aluminium sulfate is mainly used as a flocculating agent in the purification of drinking water^[2][3] and waste water treatment plants, and also in paper manufacturing.

Aluminium sulfate is used in water purification and as a mordant in dyeing and printing textiles. In water purification, it causes impurities to coagulate which are removed as the particulate settles to the bottom of the container or more easily filtered. This process is called coagulation or flocculation