Gallium nitride (GaN) is a promising material for high power and high frequency devices, and the etching processes are necessary in bipolar device fabrication. Inductively coupled plasma (ICP) etching is one of the plasma etching technique which forms damaged layer on surface of GaN. In this work, we have measured the excess carrier lifetime in ICP etched GaN with the microwave photoconductivity decay (-PCD) method. We analyzed deep levels introduced by ICP etching by measuring temperature dependence of decay curves. We also discussed about effects of annealing by observing the excess carrier lifetime.