The 1×1 magnesium octahedral molecular sieve (Mg-OMS-7), utilizing as cathode material in aqueous rechargeable magnesium ions batteries, is synthesized by a simple one-step hydrothermal method. Meanwhile, by changing the concentrations of H2SO4, the Mg-OMS-7 materials with controllable size and shape are obtained. To check the structure and morphology, the host materials are measured by X-ray power diffraction, scanning, transmission and high-resolution transmission electron microscopy. The electrochemical reaction mechanism is examined by cyclic voltammetry and X-ray photoelectron spectroscopy. The Mg-OMS-7 changes the morphology from micro-rugby to nano-club by controlling the concentrations of H2SO4. The nano-club Mg-OMS-7 which obtained by the 1.6moldm−3 H2SO4 owns a more uniformly distribution and smaller size, which provides the shorter route for magnesium ions insert/deinsert into/from the lattice of host material and exhibits the better rate ability and cycle performance. The initial discharge capacity of this electrode can obtain 283.1mAhg−1 at the current density of 10mAg−1 in the 0.2moldm−3 Mg(NO3)2 aqueous electrolyte and the specific capacity retention rate is 94.1% after cycling 200cycles at 100mAg−1 in the 0.5moldm−3 Mg(NO3)2 electrolyte.