In this study, lightweight alumina containing nanoscale intracrystalline pores was fabricated by introducing zirconia sol and alumina sol into alpha-Al2O3 micropowder. The effects of zirconia sol on the sintering behavior of lightweight alumina were also investigated. With the introduction of zirconia sol, the grain growth and phase transformation of nano-alumina are delayed. Therefore, the structure of the nanoscale pores between nanoparticles can be stabilized during heat treatment, and numerous nanoscale intracrystalline pores with diameters in the range of 50-300 nm are trapped in the alumina grains. Because of the existence of these nanoscale intracrystalline pores, the thermal conductivity of lightweight alumina decreases significantly. Lightweight alumina with the addition of 0.75 wt% zirconia sol exhibits 31% lower thermal conductivity compared to alumina without zirconia sol.