The anharmonic effect of rate constants is studied in regard to the unimolecular dissociation reaction of ethoxy radical. Due to the high strain energy of the isomerization transition states of ethoxy radical, the present Letter only deals with two dissociation channels, the C-C bond and the C- H bond scission, with the YL method. Our results show that the calculated harmonic rate constants are in reasonable agreement with the values from earlier theoretical studies. It turns out in particular that the anharmonic effect is not evident at either low energy or low temperature, while it becomes prominent with increasing energy and temperature. (C) 2010 Elsevier B.V. All rights reserved.