A reducing agent (reductant) is the reactant that donates electrons in a redox reaction and is therefore itself oxidised. By giving electrons to another species, it causes that species to be reduced. Reactive metals such as sodium are good reducing agents; a reducing agent contrasts with an oxidising agent, which accepts electrons.

还原剂是氧化还原反应中提供电子的反应物,因而自身被氧化。它通过把电子给予另一物质,使该物质被还原。钠等活泼金属是良好的还原剂;还原剂与接受电子的氧化剂相对。