A highly conductive silver (Ag) film or pattern was prepared on a poly(ethylene terephthalate) (PET) substrate by using room-temperature sinterable silver nanoparticle (AgNP) ink without any thermal treatment. The most critical factor in the room-temperature sintering of the AgNP ink was the molecular weight of the poly(N-vinylpyrrolidone) (PVP) ligand. AgNP-10 ink having a PVP ligand with the lowest molecular weight of 10000 Da produced a conductive Ag film with 6.3% of the conductivity of bulk silver without any post-treatment such as heating.