An environmentally friendly antisolvent approach, which involves only biocompatible chemicals and mild processing conditions, was developed to prepare various ZnO nanostructures including twin-cones and nanorods with controllable dimensions. The method was based on the dissolution of ZnO powders in a deep eutectic solvent (DES), followed by precipitation of ZnO nanostructures from the DES upon introduction of an antisolvent. It is the first example of the room temperature ionic liquid based antisolvent process for preparation of nanomaterials. Through suitably modulating the processing conditions, such as the ethanol content of the antisolvent and the injection time of the ZnO-containing DES, the morphology of the resulting ZnO nanostructures can be readily controlled. Anisotropic crystal growth was achieved without severe reaction conditions, such as high temperatures and high vacuums, or use of environmentally harmful chemicals, such as long carbon chain surfactants and capping reagents. The present method can be readily extended to produce versatile nanostructures of other functional materials.