We demonstrate the surface plasmon (SP)-enhanced flip-chip blue light-emitting diodes (LEDs) having silver (Ag) disks in the p-GaN layer. The optical output power of an SP-enhanced flip-chip LED with Ag disks is increased by 45% at 20mA without showing any degradation of electrical characteristics, compared with that of a conventional flip-chip LED. The increase in optical output power is attributed to the improved internal quantum efficiency of LEDs because of the increase in the spontaneous emission rate by the resonance coupling between the excitons in multiple quantum wells and the SPs in the Ag disks.