Reduction of AgNO3 by sodium borohydride in the presence of quaternary ammnoium disulfide gave a stable aqueous dispersion of silver nanoballs. The obtained Ag nanoballs showed a strong plasmon absorption peak, indicating that they consisted of metal Ag, although the counteranion of the stabilizer was Br-. They are obtainable in a powder form by reprecipitation and can be kept without any change under air. Redispersibility of the obtained powder into water was high, and even in slightly acidic condition, they can be kept stably for more than a week. The stabilization mechanism is also discussed.