The aim of this work was to prepare silver nanowires with less than 40 nm of diameter and more than 1,000 of aspect ratio using poly(vinylpyrrolidone-co-vinylimidazole) (poly(VP-co-VI)) as a new capping agent. poly(VP-co-VI) can be adjusting dimension of silver nanowires by changing the molar ratio of poly(VP-co-VI) from 4:1 to 128:1 (VP:VI). Poly(VP-co-VI) are synthesized by free radical polymerization, which α, α’-azobis(isobutyronitrile) (AIBN) was used as an initiator. Successful synthesis of poly(VP-co-VI) was confirmed by fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance spectrometry (1H-NMR). Using this poly(VP-co-VI) as a new capping agent, silver nanowires synthesized by two kinds of polyol processes. One was progressed for optimizing the content of each component and fixing the molar ratio of poly(VP-co-VI). And the other was progressed to synthesis silver nanowires with less than 40 nm of diameter and 1,000 of aspect ratio on large scale. Synthesized silver nanowires of about 38 nm diameter and 45 μm length and 1,227 of aspect ratio on large scale were characterized by laser scanning microscopy (LSM), scanning electron microscopy (SEM), transmittance electron microscopy (TEM) and X-ray diffraction (XRD).