a conductive ink formuation comprising metal nanoparticles and the preparation of the metal nanoparticles therein are disclosed . the ink formulation comprises at least one type of metal nanoparticles and solvent , which is to adjust the viscosity and surface tension of the ink formulation as well as the aggregation of the metal nanoparticles . the ink formulation is stable and demonstrates optimal performance , such as , improved jetting performance and good wetting property . the ink formulatin can be printed on a substrate and be further processed by sintering . the resultant film is of high conductivity . since the annealing temperature in the present invention is relatively low , the fabrication process is compatible with plastic substrate used for flexible electronics .