The tribological behavior of well-aligned carbon nanotube (CNT)/alumina nanocomposites was studied at multiple length scales. Pin-on-disk, microscratch and atomic force microscopy were used to test three nanomaterials: alumina matrix, thin-walled and thick-walled CNT/alumina composites. This work demonstrates that the frictional coefficient of the composites tested at all the length scales depends on the buckling behavior of the nanotubes and applied loading. Analysis is presented to assess the role of CNT buckling in determining the friction. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.