Zirconia-mullite nano-composite ceramics were fabricated by in-situ controlled crystallization of amorphous bulk, which was obtained by the controlled cooling quenching of the 1650～1700℃ melt. The ultra-fine zirconia-mullite composite ceramics were prepared from the amorphous bulk treated at 980 ℃ for nucleation, then treated at 1140℃for crystallization. The phase transformation were examined using differential scanning calorimetry (DSC) and X-ray diffraction (XRD); The microstructural features were evaluated using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX) and transmission electron microscopy (TEM). The mechanical properties were also determined using the method of Vickers indentation. It was founded that with more TiO2 addition, the starting temperature of t-ZrO2 and primary mullite formation became lower, and partial Ti4+ entered into the mullite structure and most Ti4+ reacted with ZrO2 to form the ZrTiO4 phase. Assessment for the mechanical properties indicated that TiO2 addition has great effects on the fracture toughness and Vicker hardness. The composites, with 3wt.％ titania addition treated at 1140℃, obtained relatively higher fracture toughness, 3.98 Mpa m1/2. Its Vickers hardness was 927.3 kgf/mm2.