Ink-jet printing of metal nanoparticles is an attractive method for direct patterning conductive metal lines owing to low-cost, low-waste, and simple process. While most of the researches here focused on novel metals such as gold and silver, we have developed a conductive ink containing copper nanoparticles as an alternative that is inexpensive conductive material. Copper particles with a size of 40-50 nm were synthesized by polyol process, from which the well-dispersed conductive ink with low viscosity was prepared. We have successfully demonstrated a direct writing of the conductive lines using Cu conductive ink. The ink-jet printed copper patterns exhibited metal-like appearance and became highly conductive upon heat treatments. The resistivity of the film reached to 17.2 mu Omega cm at 325 degrees C for I h in vacuum. (c) 2006 Elsevier B.V. All rights reserved.