Stoichiometric magnesium aluminate spinel (MgAl2O4, MA)-samarium aluminate (SmAlO3, SA) ceramics have been prepared at 1580°C for 4h from calcined magnesia (MgO), commercial alumina (Al2O3) and samarium oxide (Sm2O3) by a single-stage in-situ reaction sintering (SIRS) method. The phase compositions, microstructures, shrinkage ratio, bulk density and cold compressive strength of the MA-SA ceramics have been investigated. The ceramics with 2.5 - 7.5 wt. % Sm2O3 are composed of MA and SA phases. The microstructures of the ceramics are dense. MA particles exist as angular shape, and their grain size varies between 2 and 10μm but the average grain size is about 5 μm. SmAlO3 particles form due to the reaction of Sm2O3 and Al2O3, and they distribute in the intergranular space of MA grains. The diameter shrinkage ratio, volume shrinkage ratio, bulk density and cold compressive strength of MA-SA ceramics are greatly improved due to the addition of Sm2O3.