一氧化二氯是氯的氧化物之一，化学式为Cl₂O。它是次氯酸的酸酐，加热时易爆炸分解，溶于水转变为次氯酸：

单质氯气通入新制的黄色氧化汞时可得到一氧化二氯，产率较高：

主要的副反应为：

工业上用氯气与湿润的碳酸钠反应制备：

也可通过液-液萃取法，从次氯酸溶液中用四氯化碳将一氧化二氯萃取出来。

Dichlorine monoxide, is an inorganic compound with the molecular formula Cl₂O. It was first synthesised in 1834 by Antoine Jérôme Balard, who along with Gay-Lussac also determined its composition. In older literature it is often referred to as chlorine monoxide, which can be a source of confusion as that name now refers to the neutral species ClO.