UV absorption spectrum of artemisinin and transient absorption spectra of various concentrations of artemisinin reacting with sodium hydroxide were measured by using an intensified spectroscopic detector ICCD.The exposure time of each spectrum was 0.1ms.Results indicate that artemisinin has an obvious UV absorption band centered at 212.52 nm and can react with sodium hydroxide easily.All absorption spectra of different concentrations of artemisinin reacting with sodium hydroxide have the similar changes,but the moment at which the changes happened is different.After adding sodium hydroxide into artemisinin in ethanol solution,there was a new absorption band centered at 288 nm appearing firstly.As reaction went on,the intensity of another absorption band centered at 260 nm increased gradually.At the end of the reaction,a continuous absorption band from 200 to 350 nm with the peak at 245 nm formed finally.No other transient absorption spectral data are available on the reaction of artemisinin with sodium hydroxide currently.The new spectral information obtained in this experiment provides very important experimental basis for understanding the properties of artemisinin reacting with alkaline medium and is useful for correctly using of artemisinin as a potential anticancer drug.