AbstractTo the best of our knowledge, few reports have been concerned with the effect of temperature on photomediated silver nanostructure growth. In this work, the shape evolution from spherical silver nanoparticles to silver nanoprisms and nanostructures in other shapes under the irradiation of a sodium lamp (λmax= 589 nm, 0.66 W/cm2) at various temperatures (i.e., 15, 40, 60, and 80 °C) were studied by recording the TEM images and time‐course UV‐vis‐NIR spectra of the silver colloids. From TEM and spectra analysis, it was found that the photomediated silver nanoparticle shape conversion process would be faster at a higher temperature, i.e., ca. 2 hours at 80 °C, and slower at a lower temperature, i.e., ca. 17 hours at 15 °C. The silver nanoplates synthesized at a higher temperature had a narrower size distribution and were thicker than those synthesized at a lower temperature. Some decahedral silver nanoparticles, about 10% of the final irradiation products, were observed in the synthesis (with a sodium lamp) at 15 °C. In order to produce a higher yield of decahedral silver nanoparticles, the sodium lamp was replaced with blue LEDs (λmax= 450 nm), which have a wavelength closer to the SPR of decahedral silver NPs (ca. 490 nm). The decahedral silver nanoparticles with a fairly narrow size distribution were obtained by irradiating the spherical nanoparticle colloids with the blue LEDs at 2 °C in the absence of PVP or other large‐molecular‐