The spherical composite powders of multi-walled carbon nanotubes reinforced alumina are prepared by sol- spray. The results show that the multi-walled carbon nanotubes are well dispersed in the composites. The analyses of the composite properties show that most of the multi-walled carbon nanotubes are distributed in a network at the grain boundaries, and a small number of them are distributed in the grains. When the mass fraction of multi-walled carbon nanotubes accounts for 0.5%, the Vickers hardness of the composite increases by 32.6% relative to pure alumina; the thermal diffusion coefficient increased averagely by 27.2% with respect to pure alumina at different temperatures. The composites are conductive at 0.5% of multi-walled carbon nanotubes, and the percolation threshold of the composites prepared by this method is 0.32 wt.% based on the fitting of the percolation conductivity theory, indicating that the multi-walled carbon nanotubes are well dispersed in the alumina matrix.