Fructose, or levulose, is the form of sugar found in fruit and honey. It is a laevorotatory monosaccharide with the same empirical formula as glucose but with a different structure. Although fructose is a hexose (6 carbon atoms), it generally exists as a 5-membered hemiketal ring (a furanose).

All fruit naturally contains a certain amount of fructose (often together with glucose), and it can be extracted and concentrated to make an alternative sugar.

Fructose is often used in food products designed for people with diabetes mellitus or who have problems with hypoglycaemia, because it is metabolised more slowly than cane sugar (sucrose) and is sweeter, so it has a smaller effect on blood-sugar levels. However, some people can react badly to fructose so it is not an option for those who need to restrict sucrose intake