The reversible intercalation of Zn2+ ions into manganese dioxide was first reported in an aqueous system and a large capacity (210 mAh g(-1)) was measured. A cycle life test was performed at 1 A g(-1), and after 50 cycles, no capacity fading was found, which indicates the good cycling properties of manganese dioxide toward the insertion of zinc ions. X-ray photoelectron spectrum measurements indicated that Zn2+ ions in the electrolyte are involved in the charge storage process of manganese dioxide. X-ray diffraction results exhibited the kinetic stability of the host structure in allowing high-capacity, single-phase, and reversible zinc-ion intercalation.