Two-dimensional X-ray absorption spectroscopy was carried out to observe the reaction distribution in a LiCoO2 composite electrode from the shift of the peak top energy in Co K-edge X-ray absorption spectra. The influence of ionic transportation to the inhomogeneous reaction was evaluated by using the model electrode, which sandwiched the LiCoO2 composite electrode between an aluminum foil and a polyimide ion blocking layer. When the model electrode was charged with the currents of 6, 9, and 12 mA cm(-2), the observed capacities were 51, 20, and 12 mAh g(-1) and the charged areas visualized from the shift of the peak top energy in Co K-edge X-ray absorption spectra were formed within ca. 700, 500, and 200 mu m from the edge of the electrode, respectively. The observed reaction distribution indicated that the electrochemically active region decreases with increasing the current density because of the large potential loss of the electrochemical processes.