The present invention relates to a method for removing cesium in a clay mineral using hydrogen peroxide. According to the present invention, cesium in a clay mineral is removed using hydrogen peroxide, which serves to induce interlayer expansion of the clay mineral to allow a cation to easily enter an interlayer of the clay mineral, and thus cesium desorption efficiency can be further improved. Also, the method according to the present invention can be efficiently used to restore soil in residential areas widely contaminated with a radionuclide when a major accident such as Fukushima nuclear accident occurs as well as various sites of atomic energy facilities contaminated with a radionuclide. Also, since radiation-contaminated soil is treated with only hydrogen peroxide and cations, secondary environmental pollution caused by wastes can be significantly reduce and the waste disposing cost can also be saved.