Electrochromism of spinel-type manganese oxide accompanying an Li+-insertion in an aqueous phase was examined ted by visual light spectrometry. An absorbance spectrum for lithiated manganese oxide gave lower absorbance in the wavelength range <700 nm than did an Li+-extracted one. The greatest difference was observed at similar to 450 nm and is explained by the difference between the spectra for Mn3+ and Mn4+. A reversible change in absorbance at 450 nm occurred with the Li+-insertion/extraction reaction. Cyclic voltammetry indicated that the absorbance change couples with the electrochemical response of the manganese oxide to Li+ ions.