The development of rechargeable magnesium ion batteries (MIBs) has received increasing attention due to its low cost, high theoretical volumetric capacities, environmental friendliness and good safety. However, one of the main challenges faced by MIBs is the difficulty in finding a suitable electrode material due to the sluggish kinetics of the magnesium ion. Herein, we report a manganese ion pre-intercalated hydrated vanadium oxide (Mn_0.04V₂O₅·1.17H₂O) as the cathode material for MIBs for the first time. Pre-intercalation of Mn²⁺ leads to excellent structural stability and allows fast (de)insertion of Mg²⁺ ions. The charge shielding effect of crystal water in the material enhances the Mg²⁺ (de)insertion kinetics and the unique nanostructure ensures the large contact area and shortens the Mg²⁺ diffusion distance between the electrode and electrolyte. Benefiting from the structure and charge shielding effect, the Mn_0.04V₂O₅·1.17H₂O nanobelts exhibit excellent cycling stability (capacity retention of 82% after 10 000 cycles at 2 A g⁻¹) and superior rate performance. These results indicate that Mn_0.04V₂O₅·1.17H₂O is a promising and attractive cathode material for MIBs.