Downsizing copper nanoparticles (Cu NPs) can effectively improve their catalytic activity, but simultaneously ensuring the structural stability is always a challenge. In this study, by laser ablating a Cu target in graphene oxide (GO) solution along with a reduction treatment, pure Cu NPs (2.0 +/- 0.4 nm) are evenly scattered on reduced graphene oxide (rGO). As-prepared Cu/l. GO nanocomposites (NCs) are applied as catalysts for 4-nitrophenol (4-NP) reduction, which display high values of mass-normalized rate constant (k/m, 3.118 s(-1) mg(cu)(-1)) and turnover frequency (TOF, 2.987 x 10(-4) mmol mg(cu)(-1) s(-1) ), over those of most reported Cu catalysts. In addition, owing to the stable conjugation between ultrafine Cu NPs and rGO, the Cu/rGO catalysts reveal good catalytic stability that the conversion efficiency of 4-NP is still over 92.0% even after 10 successive cycles. (C) 2020 Elsevier Inc. All rights reserved.