Silver nanowires with a monoclinic structure (mono-Ag NWs) were fabricated by a thermal evaporation method for the first time. The crystal lattice parameters of the mono-Ag NWs were calculated using the UnitCell program. They are as follows: a = 0.303 nm, b = 1.140 nm, c = 0.292 nm, and beta = 118.5 degrees. In situ annealing experiments revealed that the as-prepared mono-Ag NWs transited to fcc-Ag NWs during annealing at approximately 1173 K for 60 s.