Aqueous colloidal forming techniques like slip/gel casting have been attempted to prepare monoliths of aluminum oxynitride (AlON) starting from the constituent raw materials of high-purity alumina and aluminum nitride. A surface treatment conducive to prevent hydrolysis of aluminum nitride in an aqueous medium was carried out before the shaping technique. The slurry, leading to an AlON composition of Al23O27N5, was prepared with high solid loading (76-80 wt%) in water and casted into molds, dried, and sintered in the temperature range 1725 degrees-1925 degrees C in a nitrogen atmosphere. AlON phase formation was followed by XRD and it was observed that phase-pure AlON was obtained at temperatures above 1825 degrees C. The samples were further characterized for mechanical and microstructural properties.