We have developed a copper metal-organic-based conductive ink which can be applied to printing and roll-to-roll processes. Metal-organics printed on flexible substrates decompose into highly conductive copper metal when annealed at above 250 degrees C. The new nano ink was prepared by mixing copper carboxylate with copper complex nano particles of a mean size below 100 nm. The viscosity of the copper ink was in the range of 10(4)-10(5) mPa s (at 50 rpm). The resistivity of the conductive film, after annealing under the condition of 3% H(2) above 250 degrees C for 20 min, was below 10 mu Omega cm and it could be further reduced to 4.4 mu Omega cm when annealed at 320 degrees C for 20 min. We successfully demonstrated a printable copper nano ink that proceeds to form highly conductive metal film when annealed at low temperature on flexible substrates. (C) 2009 Elsevier B.V. All rights reserved.