We perform first-principles calculations on single- or dimer-Cu-absorbed-BN sheet. It was found that the band gap of BN sheet was reduced due to the emergence of certain impurity states arisen from Cu atom. The value of band gap depends on the adsorption configuration. Unpaired electron in absorbed single- Cu atom is polarized causing a magnetic moment of 1.0 mu(B), while no magnetic moment has been detected after dimer-Cu adsorption. Comparing the analogous carbon nanostructures, Cu-absorbed BN sheet is more resistant to oxidation and thereby is more experimentally accessible. (C) 2010 Elsevier B. V. All rights reserved.