Abstract: A simple and exact method, spectrophotometric method, for determination of trace lithium was developed. Thoron was used as the developer, 20% potassium hydroxide was used to adjust alkalescence of the solution, and the lithium-thoron complex was developed in acetonewater medium. In order to determine trace lithium in aqueous phase and organic phase, the operation procedure was established. Conformity to Beer’s law was obtained within the scope of 0.01~0.5 g/L of lithium at the sampling of 10 μL. The precision is better than 2.0% and 4.0%, respectively for the determination of lithium in aqueous and organic phases.