Using a unique technique, we formed a thin layer of ice on steel surface at temperature as low as 123 K in an ultrahigh vacuum. We investigated the frictional behavior of such a thin ice layer in the same UHV using a pin-on-disk friction tester. The sample surfaces were monitored in situ using X-ray Photoelectron Spectroscopy (XPS). Testing data showed that the friction coefficient was a linear function of temperature. This study indicates that the sliding motion is lubricated by a frictionally melted liquid layer. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.