Two different InGaN/GaN multiple-quantum well (MQW) microdisk light emitting diodes (mu-LEDs) with different In compositions in the MQW were fabricated. The optical output power was greatly increased with a reduction of LED size. This can be attributed to the enhanced current density and internal quantum efficiency in mu-LEDs. The peak shift and the enhancement of output power were larger in mu-LED with a higher In composition in the MQW. These can be explained by a reduced piezoelectric field due to a partial strain relief and also more efficient carrier confinement due to a higher In composition in the MQWs. (C) 2005 The Electrochemical Society.