Electrochemical lithium intercalation into highly oriented pyrolytic graphite and natural graphite powder was investigated using in situ Raman spectroscopy. Three plateaus were observed on the charging curve for both samples. From the Raman spectral changes the first plateau was assigned to a phase transition from dilute stage 1 to stage 4, the second from a stage 2 phase to another stage 2 phase, and the third from stage 2 to stage 1, which are in good agreement with Dahn’s results by in situ x-ray diffraction. The spectral changes associated with the phase transitions occurred reversibly during a charge and discharge cycle. It was shown from the Raman spectral changes of the HOPG electrode that the electrode potential during the electrochemical intercalation is determined by the surface stage of graphite intercalation compounds.