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