The voltage delay of the 70 mah cadmium-mercuric oxide button cell was severe at low temperatures, especially when it was kept several hours at -400℃. As proved by previous work, the delay phenomenon is caused by the mercuric oxide electrode, but not the cadmium electrode, Galvanostatic and potentiodynamic techniques were used to investigate the electrode reactions in mercuric oxide cathodes. The delayed voltage of the mercuric oxide cathode increased with decreasing temperature or increasing discharge rate, and roachod a maximum value which was almost independent on temperature, but dependent on the conducting material used in the mercuric oxide electrode (e. g. about 140 mV for Ni and 40 mV for Ag, respectively). Nylon felt containing PVA and CMC was used as diaphragm in the cell. It appreciably increased delayed voltage after the cell had been stored for 1 month. The voltage delay of the cell during constant current discharge is due to the slowness of formation of nuclei on the substrates of the mercuric osido cathode, and the maximum delayed voltage corresponds to the overvoltage of forming smallest nuclei on the cathode.