Single-walled carbon nanotubes (SWCNTs) were used to convert insulating nanoceramics to metallically conductive composites. Dense SWCNT/Al2O3 nanocomposites with CNT contents ranging from 5.7 to 15 vol % and with nanocrystalline alumina matrices have been fabricated by spark-plasma-sintering that retains the integrity of SWCNT in the matrix. The conductivity of these composites increases with increasing content of CNTs. The conductivity has been increased to 3345 S/m in the 15 vol % SWCNT/Al2O3 nanocomposite at room temperature. This is an increase of 13 orders of magnitude over pure alumina and of more than 735% over previously reported results in CNT–ceramic composites. © 2003 American Institute of Physics.