The synthesis and characterization of Co,Al Layered Double Hydroxides (LDHs) containing carbonate is reported. The solids have been submitted to several thermal treatments, hydrothermal and microwave-hydrothermal, modifying both the treatment time and temperature, with the main aim of studying their influence on the crystallinity of the solids and on the stabilization of divalent cobalt oxidation state. The results show that whichever the temperature and time used the only phase detected was the hydrotalcite, and that the cobalt cations keep the divalent oxidation state.