Three-dimensionally hierarchical flowerlike MgO hollow spheres with an extremely high surface area of 343 m(2) g(-1) were prepared through a facile and environmentally friendly solvothermal route. The maximum adsorption capacity at natural pH reached 569.7 mg g(-1) for the removal of arsenic in water, which is the highest among all of the reported adsorbents. In addition, flowerlike MgO hollow spheres also displayed excellent catalytic activity and stability for the Claisen-Schmidt condensation reaction as a solid base catalyst.