Duplex spinel-ZrO2 ceramic composites were produced by an emulsion-hot kerosene drying technique. The sintered duplex spinel-ZrO2 ceramics which had the composition of 55 wt % Al2O3-20 wt % ZrO2-25 wt % MgO, consisted of a spinel matrix, whose grain size was in the range of 1.5 to 2.0 mu m, and uniformly dispersed zirconia agglomerates having grain sizes ranging from 1.0 to 2.0 mu m. Zirconia agglomerates began to appear at a temperature of 1500 degrees C and the duplex spinel-ZrO2 structure was formed with the weight ratio of Al2O3/MgO being within 1.67 to 2.20 and the amount of ZrO2 addition being within 5 to 25 wt %. The relative density, fracture toughness, flexural strength, and critical temperature difference of the spinel-ZrO2 composite were 97.8 %, 1.98 MPam(0.5), 390 MPa, and 275 degrees C, respectively.