Multiphase ceramic composites with improved mechanical properties and high-temperature stabilities resulting from minimized grain sizes due to extended diffusion distances are introduced. Four-phase (quadruplex) composites of 25 vol% Al2O3-25 vol% NiAl2O4-25 vol% TiC-25 vol% "ZrO2"; 30 vol% Al2O3-30 vol% NiAl2O4-10 vol% TiC-30 vol% "ZrO2"; and 50 vol% Al2O3-20 vol% NiAl2O4-10 vol% TiC-20 vol% "ZrO2" as well as a five-phase (quintuplex) composite of 20 vol% Al2O3-20 vol% TiB2-20 vol% TiC-20 vol% ZrB2-20 vol% "ZrO2" were fabricated using hot-pressing procedures. The 25 vol% Al2O3-25 vol% NiAl2O4-25 vol% TiC-25 vol% "ZrO2"double dagger composite, hot pressed at 1600 degrees C for 1 h in an Ar atmosphere, had three-point bend strength, hardness, and toughness values of 984 MPa, 1251 kg/mm(2), and 4.74 MPa.m(1/2), respectively. The chemically compatible, quintuplex composite consisting of 20 vol% Al2O3-20 vol% TiB2-20 vol% TiC-20 vol% ZrB2-20 vol% "ZrO2" was hot pressed at 1800 degrees C in an Ar atmosphere for 5 h and it had hardness, bend strength, and toughness values of 1707 kg/mm(2), 714 MPa, and 5.12 MPa.m(1/2), respectively. The four- and five-phase composites, heat-treated under an Ar atmosphere at 1600 degrees C for 100 h, each showed high-temperature stabilities without any severe changes in the microstructural and mechanical properties.