Poly(methyl methacrylate) (PMMA) substrates containing silver nanowires (Ag NWs) were fabricated by using a transfer method. Ag NWs with a length of 20 μm and a width of 80 nm were synthesized by using a modified polyol process. Ag NW electrodes with a high surface roughness value on glass substrates were significantly improved by using both a transfer method and a poly(3,4-ethylenedioxythiophene):polystyrene sulfonate layer coating. The peak-to-valley roughness of the Ag NWs decreased from 210 to 26 nm resulting from the filling of the PMMA into the vacancies among the Ag NWs, and the corresponding root-mean-square roughness decreased from 74 to 6 nm. Atomic force microscopy images showed a dramatic decrease in the surface roughness of the PMMA substrates containing Ag NWs. The optical transmittance and the sheet resistance of the optimized Ag NW-embedded PMMA substrates were 80% and 14 Ω/sq, respectively.