Multimetallic anionic clays (MACs) are prepared using economical raw materials or reactants and a procedure for obtaining a series of multimetallic mixed oxides derived from the thermal decomposition of the MACs which comprises: (1) dissolving water-soluble bimetallic and/or trimetallic sources in water, (2) dispersing and homogenizing separate water-insoluble divalent and/or trivalent metal precursors with a high-speed stirrer in order to obtain small and reactive particles; depending on the nature of the water-insoluble divalent and/or trivalent metal precursors, this process can be adjusted to a desired pH, (3) adding the suspension obtained in (2) to solution (1) with the reaction medium still dispersed to facilitate solid particle's reduction/dissociation, and (4) afterwards the slurry is aged for several hours and finally dried. This process enables raw materials or reactants to be easily handled, and eliminates unit operations involving product washing and/or purification steps.