Abstract: A process for removing hydrogen peroxide in water which comprises bringing water for treatment containing hydrogen peroxide into contact with a catalyst for decomposing hydrogen peroxide obtained by depositing nano-colloid particles of a metal of a platinum group which have an average diameter of 1 to 50 nm to be supported on a support; and an apparatus for removing hydrogen peroxide which comprises an apparatus for decomposing hydrogen peroxide packed with a catalyst obtained by depositing nano-colloid particles of a metal of a platinum group which have an average diameter of 1 to 50 nm to be supported on a support, a means for supplying water which supplies water for treatment containing hydrogen peroxide to the apparatus and a means for discharging water which discharges the water from the apparatus after being brought into contact with the catalyst. Hydrogen peroxide in water for treatment can be removed rapidly and surely.