The dispersing behavior of MgO-doped mullite suspension suitable for the production of reticulate ceramics by sponge impregnation was studied. Three deflocculants were tested and the optimum dispersing conditions for the mullite suspension were found. Electrokinetic studies of magnesia in water evidence that it undergoes pronounced solubilization that strongly affects the performance of the mullite suspension when added at the 1 wt% concentration, in terms of solid loading and aging effects. The optimum composition of the slurry was found, reticulate mullite samples were produced, and the green and sintered bodies were characterized.