To stably perform an analysis using hydrogen peroxide as a reagent without affecting the principle of the analysis by adding an aqueous solution to the dry hydrogen peroxide adduct of a component such as a carboxylic acid (salt), when the measurement is carried out.

This method for analyzing by using at least a peroxide as an analyzing reagent comprises adding an aqueous solution just at the time of a measurement to the dry hydrogen peroxide adduct of at least a component such as a monocarboxylic acid of formula I [R1 is H, CH2OH; R2 is H, NH2, OH, CH2OH; R3 is H, CH3, a group of formula II ((x) is 1-5), etc.], a carboxylic acid such as pyruvic acid, the salts of the carboxylic acid, phosphoric acid, the salts of the phosphoric acid, a sulfonic acid or the salts of the sulfonic acid, and using the generated peroxide as an analyzing reagent. Thereby, the analyses in a wide field such as clinical examinations and environmental tests can stably be carried out in a state little in the affection on the principle of the analysis.