Silver nanowires were synthesized by solvothermal method through reducing silver nitrate (AgNO3) with ethylene glycol (EG) in the presence of polyvinylpyrrolidone (PVP). In order to prevent the agglomeration of Ag+ in the initial Ag seeds formation, sodium chloride (NaCl) was added into the solution to form AgCl colloids. By dissolving AgCl in the late stages, Ag+ ions were released into the solution. So the diameters of silver nanowires could be controlled by modifying the PVP concentration. The effect of reaction time, reaction temperature, and for first time purity of EG over the shape of resulted silver nanowires were investigated. The wire, sphere and tree-like nanostructures were formed with changing these parameters. The structural and optical properties of the silver nanostructures were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and UV–visible absorption spectrophotometer. In order to synthesis silver nanowires with smaller diameters and longer lengths, the optimum molar ratio of PVP/AgNO3, reaction time, reaction temperature, and EG purity were found to be 1.5, 2.5 h, 160 °C, and 99.5%, respectively.