In this study, poly(ethylene glycol) (PEG)-coated silver nanowires (SNWs) have been hydrothermally prepared at a very slow rate, in which PEG was used as both a mild capping agent and a weak reductant. The as-prepared SNWs have been characterized using scanning electron microscope and transmission electron microscope (TEM), which showed that the SNWs are usually longer than 100 μm and their diameters (each SNW has a uniform thickness) vary mainly in the range of 80-300 nm. Surprisingly, some of these SNWs connected by their two ends to form some close-looped SNWs, which has not been previously reported. The existence of close-looped SNWs supports the mechanism that nanowires can evolve from fusion of some nanoparticles and/or shorter nanorods. Careful TEM characterization and selected area electron diffraction revealed that the SNWs kept a fivefold twinned structure, which was inconsistent with some previous observations that a long-time incubation would lead to the disappearance of this twin structure. This study demonstrates the situation that further investigation is still needed for understanding the structure transformation of SNWs.