A multiscale approach using Bridging Cell Method ( BCM) is applied to simulate the combined effect of temperature and alumina's common structural nanodefects such as nanovoids, precracks, and Mg impurities on the mechanical response of single crystal C-plane and M-plane sapphire. The BCM model consists of three domains of continuum, bridging, and atomistic, where the whole system is solved in a finite element ( FE) framework. Interatomic interaction potentials and temperature-dependent formulations are incorporated in the atomistic domain to conduct simulations for structures containing nanodefects at a range of finite temperatures from 300 to 1600 K. The results are compared for each case to analyze the effect of temperature and nanodefects. Mechanical response of the material is presented and discussed with respect to ultimate tensile strength ( UTS), stress distribution and elasticity. Results show different material behavior for C-plane and M-plane under the same biaxial loading conditions but containing different nanodefects. Precracks are found to be the most critical defects for both systems, which significantly reduce structural strength.