The output enhancement of a green InGaN/GaN quantum-well (QW) light-emitting diode (LED) through the coupling of a QW with localized surface plasmons (LSPs), which are generated on Ag nanostructures on the top of the device, is demonstrated. The suitable Ag nanostructures for generating LSPs of resonance energies around the LED wavelength are formed by controlling the Ag deposition thickness and the post-thermal-annealing condition. With a 20 mA current injected onto the LED, enhancements of up to 150% in electroluminescence peak intensity and of 120% in integrated intensity are observed. By comparing this with a similar result for a blue LED previously published, it is confirmed that surface plasmon coupling for emission enhancement can be more effective for an InGaN/GaN QW of lower crystal quality, which normally corresponds to the emission of a longer wavelength.