Abrasive is one of key influencing factors on the surface quality during the chemical mechanic polishing (CMP). alpha-Alumina particles, as a kind of widely used abrasive in CMP slurries, often cause to surface defects because of its high hardness. In the present paper, a series of novel alumina/silica core-shell abrasives in slurries were described. The CMP performances of the alumina/silica core-shell abrasives on hard disk substrate were investigated by using a SPEEDFAM-1613-4M CMP equipment. Experimental results indicate that the CMP performances are strong dependent on the coated SiO2 content of the alumina/silica composite abrasives. Slurries containing the alumina/silica composite abrasives exhibited lower surface roughness and waviness as well as lower topographical variations and less scratch than that containing pure alumina abrasive under the same testing conditions. (c) 2007 Elsevier B.V. All rights reserved.