Galactose (/ɡəˈlæktoʊs/, galacto- + -ose, “milk sugar”), sometimes abbreviated Gal, is a monosaccharide sugar that is about as sweet as glucose, and about 65% as sweet as sucrose.

It is an aldohexose and a C-4 epimer of glucose.

A galactose molecule linked with a glucose molecule forms a lactose molecule.