The electrochemical properties of a thin-film LiMn2O4 electrode were studied in an aqueous medium. The studies were done in a saturated aqueous medium to increase similarity of the electrolyte solution with a non-aqueous medium. The apparent diffusion coefficient was calculated and discussed for different potentials at the aqueous electrolyte. In addition, stability of the thin solid film was investigated during potential cycling, which indicates that the electrode is highly stable in aqueous medium as well as in non-aqueous media. The obtained results from electrochemical measurements indicate that the properties of the thin-film LiMn2O4 electrode in aqueous medium are similar to those that have been found in non-aqueous media.