The dissolution process of Mn from LiMn2O4 cathode into an electrolyte solution accompanied on electrochemical cycling at various temperature was studied for the first time by in situ methods using a combination of total reflection X-ray fluorescence (TXRF) analysis and a capillary technique. When the in situ cell was cycled at 50°C, the Mn concentrations measured on the 5th, 10th and 15th cycles were determined to be 11, 56 and 393ppm, respectively. The concentration of Mn in the cell was shown to be the highest at the center of both electrodes. It was also found that dissolution of Mn from the cathode material takes place during the charge rather than the discharge process. Mn K-XANES (X-ray absorption near-edge structure) spectra of the electrolyte solution revealed that Mn exists as Mn2+.