A novel methodology for the production of mullite/zirconia nanocomposites is proposed, starting from a mixture of a preceramic polymer containing gamma-Al(2)O(3) and ZrO(2) nanosized powders as fillers. After heat treatment at 1350 degrees C in air crack-free monoliths with nanometric grain size for both matrix and reinforcement phase were obtained. Different commercial ZrO(2) nanosized powders were tested, and indentation tests showed a remarkable increase of toughness due to a very effective transformation-toughening mechanism. Moreover, the additional introduction of a small quantity of TiO(2) nanosized powder led to an increase in density of the nanocomposites at relatively low sintering temperature.