By bubbling air or nitrogen gas, 1,4-dioxane in waste water was vaporized at 298-357 K. The vaporization behavior could be explained by means of the Henry constant. By UV irradiation of the gaseous phase containing 1,4-dioxane, a constant amount of 1,4-dioxane was decomposed per unit time regardless the mean residence time in an UV irradiation vessel. By appyling the gas bubbling-UV irradiation treatment to the waste water eluted from solid-waste reclaimed land, it was verified that 1,4-dioxane in the solution was sufficiently decomposed. As UV irradiation products, acetic acid, acetol, ethylene glycol monoformate and ethylene glycol diformate were detected. These products were presumed to be formed by oxidative cleavage of the 1,4-dioxane ring.