Abstract: 30 vol%Al₂O_3P/Al-2.26Mg-0.63Si composite was fabricated by the Pressure Infiltration Method for investigating the aging behavior of the composites with sub-micron Al₂O₃ particles. The corresponding matrix alloy was obtained by tailoring the Mg and Si contents of 6061Al. The aging behaviors of the composites and the corresponding matrix alloy were investigated by means of Brinell hardness test，SEM and TEM. The results show that the aging behavior of the matrix alloy of Al-2.26Mg-0.63Si is visible and the peak-aging time is put ahead with the aging temperature rise. The aging softening phenomenon appears at 190℃. The addition of sub-micron Al₂O₃ particles rest rains strongly the precipitation process within the matrix. There are no obvious aging peaks to appear in the aging-hardening curves of the composites. TEM observation shows that a mass of MgAl₂O₄ spinel forms in the interfaces , and atoms cannot diffuse efficiently for little dislocations existing in the matrix alloy. Therefore，GP zone does not grow-up at over-aged course within the composites，and the aging precipitation is restrained.