PURPOSE: To obtain a stable peroxide-contg. liquid over a long period of storage without causing precipitation even under the coexistence of calcium and sodium ions by incorporating a specified compd. in the peroxide-contg. liquid.

CONSTITUTION: Compounds shown in the formula I (where A is carboxyl group, phosphoric acid group and their salts, X is hydroxyl group and its salt; (r), (l) are 1, 2; (n) is 1W4; (m) is 0W3; B is H, halogen atom, lower alkyl, hydroxyl group, carboxyl group, phosphoric acid group and their salts) are incorporated in a peroxide-contg. liquid. As the preferable compds. to be used shown in the formula I , the compds. shown in the formulae II, III, IV are exemplified. The above-mentioned peroxide-contg. liquid is preferably used in combination with a chelating agent according to necessity in addition to the compds. shown in the formula I . And the generation of precipitate can be minimized considerably in this case.