Abstract: The formation mechanism of aluminum borate in the combustion synthesis of Al₂O₃/B₄C composite was proposed.Based on the formation mechanism several approaches taken to eliminate them are discussed.The X-ray analysis and SEM observation of the SHS products at various conditions reveal that the holding at elevated temperature before ignition is conducive to the formation of Al₄B₂O₉.The unconverted B₂O₃ is the major cause of the formation of Al₁₈B₄O₃₃if the reaction proceeds in the SHS mode.The amount of Al₁₈B₄O₃₃formed is very sensitive to the excess B₂O₃ to the stoi-chiometry 4Al+2B₂O₃+C and influenced by the size of B₂O₃ powder.The high dispersion of the reactants is helpful in prompting the thermite reaction to consume B₂O₃ and hence inhibiting the aluminum borate formation.