This work developed a two-steps synthesis of silver-copper composite nanoparticles by dextrose reduction and with the addition of urea. Wherein, a part of the silver nanoparticles were prepared at first and were characterized by TEM image and EDX analysis, such that they could be the seeds for following the reduction of silver incorporated with copper in the colloids. In addition, the results of the study on thermal behavior of these kinds of particles has shown that with 5 h-heating, the copper on the particle surface would be partially oxidized at 200 degrees C, and complete oxidation of all the copper inside the composite occurred at 350 degrees C. After proper purification and concentration, 20 wt% Ag-Cu colloids as an ink was filled into a felt-tip pen and written on a substrate to make conducting lines. We also have demonstrated that the addition of copper to silver was helpful in reducing the electrical migration encountered by pure silver conducting lines. (C) 2010 Elsevier Ltd. All rights reserved.