Dehydration synthesis reactions are reactions in which molecules combine by the removal of a H atom and an OH group between them, which together form a molecule of water, ##"H"_2"O"##

Dehydration synthesis reactions are reactions in which molecules combine by the removal of a H atom and an OH group between them, which together form a molecule of water, ##"H"_2"O"##. Therefore, a new molecule is synthesized while the reacting molecules lose a molecule of water (dehydration) between them.

For example, the formation of maltose (malt sugar) from two molecules of glucose is a dehydration synthesis.

Most biomolecules, such as carbohydrates, triglycerides, proteins, and nucleotides are formed in this way.