Abstract: HT5"SSSlightly acid electroylzed water(SAEW) was developed in Japan in 1990s. It was made by electrolysis of dilute hydrochloric acid. The main bactericidal component was hypochloric acid (HClO). It has the characteristics of strong bactericidal ability, wide bactericidal range, no pollution, no residue, safety, reliability, innocuity to the human body, no irritation of skin, convenient preparation, low price and so on. Since 1997, some researchers have studied its germicidal efficacy and safety. In 2002, SAEW was designated as food additive in Japan with the name of hypochlorous acid water, afterwards it was put into use in food, animal husbandry, agriculture and other fields. In recent years, its research in the field of medical treatment has also been carried out. This article introduced SAEW from the aspects of its performance, oral application, safety and so on.