Ultrafast electronic relaxation measurements in thiol-capped Au-11 reveal an excited state lifetime of >500 ps, similar to Au-13 and Al-28. Upon extended exposure to laser light, a small amplitude, fast relaxation component was observed and attributed to formation of larger particles or aggregates. The long lifetime, combined with a lack of excitation intensity dependence, indicates that Au-11 behaves more molecule-like rather than a typical, bulk-like gold metal nanoparticle. The main relaxation pathway is proposed to be non-radiative mediated by a large number of surface trap states. (C) 2003 Elsevier B.V. All rights reserved.