A very fine and pure mullite powder of the stoichiometric composition was prepared from aluminium isopropoxide and tetraethylorthosilicate by an alkoxide hydrolysis method using NH4OH as a catalytic agent. The gel powder obtained from the hydrolysis was calcined at 80$0^{circ}C$ and 125$0^{circ}C$. The average particle sizes of the powders calcined at 80$0^{circ}C$ and 125$0^{circ}C$ were 0.19${mu}{ extrm}{m}$ and 0.25${mu}{ extrm}{m}$, respectively. The specific surface areas of the powders calcined at 80$0^{circ}C$ and 125$0^{circ}C$ were 114.7$m^2$/g and 20.6$m^2$/g, respectively. The bending strength and fracture toughness of the mullite ceramics sintered at 1$650^{circ}C$ were 263.1MPa and 2.30MPa.m1/2 respectively.