Flower-like MgO was synthesized by spray drying combined with heat treatment. The morphologies of MgO can be controlled by adjusting calcination temperature. The adsorption properties of MgO powder as adsorbent to Congo red were studied. When calcination temperature was 350°C, a flower-like MgO nanostructure with a high BET surface area of 180.5m²⋅g⁻¹ was obtained, and the saturated adsorption capacity of Congo red solution was about 2140mg⋅g⁻¹. Furthermore, the adsorption model was explored, and the result shows that the adsorption process accords with Langmuir adsorption model. The high uptake capability of the as-prepared flower-like MgO makes it as a potentially attractive adsorbent for the removal of organic dyes from water.