Aqueous zinc (Zn)-ion batteries are gaining considerable attention as grid-scale energy storage systems due to their advantages in rate performance, cost, and safety. Here, we report a layered manganese oxide that contains a high content of crystal water (∼10 wt%) as an aqueous zinc battery cathode. The interlayer crystal water can effectively screen the electrostatic interactions between Zn 2+ ions and the host framework to facilitate Zn 2+ diffusion while sustaining the host framework for prolonged cycles. By virtue of these 'water' effects, this material exhibits a high reversible capacity of 350 mA h g −1 at 100 mA g −1 , along with decent cycling and rate performance, in a two-electrode cell configuration. Density functional theory (DFT) calculations and extended X-ray absorption fine structure (EXAFS) analyses jointly reveal that upon Zn 2+ ion intercalation, a stable inner-sphere Zn-complex coordinated with water molecules is formed, followed by the formation of a Zn-Mn dumbbell structure, which gives a clue for the observed electrochemical performance. This work unveils the useful function of crystal water in enhancing the key electrochemical performance of emerging divalent battery electrodes. Crystal water improves electrochemical performance of the layered manganese oxide for aqueous rechargeable zinc batteries.