Hydrolysis is a chemical reaction during which one or more water molecules are split into hydrogen and hydroxide ions which may go on to participate in further reactions.[1][2] It is the type of reaction that is used to break down certain polymers, especially those made by step-growth polymerization. Such polymer degradation is usually catalysed by either acid e.g. concentrated sulphuric acid [H2SO4] or alkali e.g. sodium hydroxide [NaOH] attack, often increasing with their strength or pH.

Hydrolysis is distinct from hydration, where hydrated molecule does not "lyse" (break into two new compounds). It should not be confused with hydrogenolysis, a reaction of hydrogen.