The Galactose is a Monosaccharide formed by 6 atoms of Carbone (figure 1), still called Hexose (sugar with 6 carbons). It is a épimère Glucose with the 4th carbon. Hexose of the family of aldoses, it is a reducing sugar, it has tendency to cycliser in a form being derived from the Pyrane: galactopyrannose (figure 2). It is found in milk in the form of lactose. Galactose does not exist in a free state. It results from the hydrolysis of the Lactose.