PURPOSE: Ag compound such as AgNO3 is treated by oxydation agent such as potassium persulfate at least two times in alkaline solution to provide two valency silver oxide having high degree of crysyallinity and low decomposition rate stability.

CONSTITUTION: 10 to 60% aqueous solution of Ag compound such as AgNO3 is treated in alkaline solution such as NaOH by potassium (sodium) persulfate for oxidation at least two times, under the condition such that in a first treatment, 5 to 10% potassium (sodium) persulfate is used at 90°C or below, in a second treatment, 2.5 to 5% potassium (sodium) persulfate is used at 70°C or below. The formed material is stable and little swellable and has high usage efficiency. It provides battery having enhanced cell capacity and long service life. It is further useful in electronic time keeper and a variety of small electronic devices.