Truncated silver nanodecahedrons (TAgNDs) and truncated silver nanoplates (TAgNPs) fabricated via chemical reduction and photochemical methods were added to poly[3,4-ethylenedioxythiophene]:poly[styrenesulfonate] (PEDOT:PSS) as dopants to promote the luminous efficiency of blue-emitting polymer light-emitting diodes (PLEDs). The differences in shape between TAgNDs and TAgNPs result in better dispersion of TAgNDs in PEDOT:PSS. Therefore, at an optimal doping concentration (the distributed density in the light-emitting region is 6.88 μg cm-2 for TAgNDs and 5.16 μg cm-2 for TAgNPs), the average current efficacy and maximum electroluminescence intensity enhancement factor for TAgND-doped PLEDs were 4.18 cd A-1 and 420%, respectively, which are much higher than those for TAgNP-doped PLEDs (1.83 cd A-1 and 200%) at a luminescence wavelength of 440 nm.