A clean method for preparing layered double hydroxides (LDHs) has been developed, featured by using the hydroxides of two different metals as starting materials by atom-economic reactions. The reactions were carried out under hydrothermal conditions in either a high pressure autoclave or a microwave digester.The compositions, structural parameters and thermal behavior of the resulting LDHs are very similar to those of materials produced by using the separate nucleation and aging steps (SNAS) method. The major advantage of the new method is that no by-product is produced, so that filtration and washing processes are unnecessary. The consequent reduction in water consumption is beneficial to the environment.