The direct synthesis of Al2O3/SiC nanopowders from the parent oxides Al2O3 and SiO2 through mullite carbothermal reduction as intermediate phase has been investigated. The effect of the amount of excess stoichiometric carbon (active charcoal, AC) as sole carbon source on the microstructure evolution has been studied. The effect of type of carbon source (AC, graphite (G), 50 wt % AC 50 wt % G mixture, 57 wt % AC 43 wt % G mixture) on the microstructure evolution was investigated using 30 wt % excess stoichiometric carbon. The effect of reaction temperature, reaction duration, initial green compact thickness, and carbon source on the mullite conversion, morphology, and surface area of the final powders has been thoroughly investigated. The calculated activation energy is in the range of 203-230 kJ mol(-1), depending on the carbon source used. The synergetic effect observed for the AC/G mixtures has been accordingly explained. (C) 2010 American Institute of Chemical Engineers AIChE J. 56: 1372-1382, 2010