In this study, Alumina (Al2O3) nanopowder associated with different values of silicon carbide nanoparticles (nanoSiC) including 0, 1.5, 3, 4.5, 6, 7.5, 9, 10.5, 12, 13.5 and 15vol% as well as 1 and 2vol% of magnesium dioxide nanoparticles (nanoMgO) were mixed in high-energy ball-mill exposed to isopropanol containing tungsten carbide (WC) balls. Obtained mixture has been dried and got forming process using cold press method. Produced samples have been sintered by hot-press technique at 1700, 1750, 1800, 1850 and 1900°C with a pressure of 30MPa. The impact of reinforcing nanoparticles and sintering temperature on mechanical characteristics of the manufactured samples such as flexural strength, fracture toughness and existing residual stress was examined as well, and their effect on grains and grain boundaries toughness have been examined. Furthermore, fracture behavior and also percentage of transgranular fracture (%PTF) or intergranular fracture were evaluated through studying the fracture surface of the samples. Results showed a considerable increase in flexural strength and fracture toughness by 473.82MPa and 5.29MPa·m1/2, respectively. Moreover, by increasing the volume fraction of reinforcements, in addition to getting finer grains in nanocomposite structures, residual stress and grain boundary toughness have been increased and grain toughness has been decreased. The fracture type was altered from intergranular state when there was no SiC to transgranular state with the increase in SiC in nanocomposite.