In this paper, molecular dynamics simulation was performed to predict the thermal conductivities of ordered mesoporous α-Al2O3. A kind of porous structure was proposed to guarantee the electrical neutrality. Based on the Matsui potential, the nonequilibrium molecular dynamics method adapted by Mller-Plathe was used to calculate the lattice thermal conductivity of mesoporous alumina along the axial direction of pore at various temperatures. Effects of pore size and porosity were also investigated. It turns out that with increasing temperature the thermal conductivity of mesoporous α-Al2O3 rises first until the temperature reaches 200–400 K, then decreases almost linearly. In addition, as the pore size gets larger, the specific surface area decreases, and the thermal conductivity increases because the boundary scattering has been weakened. On the other hand, the number of phonons in the pore wall decreases greatly with increasing porosity, thus dramatically reducing the thermal conductivity of the mesoporous material. Range analysis shows that the porosity is more influential than the pore size on the thermal conductivity of mesoporous materials.