This study aims to investigate the impact of irradiation on the behavior of Polyamide (PA) composite reverse osmosis (RO) membranes. Irradiations were performed for two doses (0.1 and 1 MGy) in wet conditions under an oxygen atmosphere, with a gamma 60Co source. Irradiation effect on RO membranes performances (NaCl rejection, permeability) was studied before and after irradiation. ATR-FTIR, XPS, AFM, FESEM microscopy, ion chromatography were also used to characterize structural modifications. Results show that NaCl rejection of RO membranes irradiated at 1 MGy decreased until 64% and permeability increased by a factor of three. Nevertheless, membranes irradiated at 0.1 MGy did not exhibit any change in theirs permselectivity properties. Advanced analysis techniques confirmed that the firsts effects of gamma rays on RO membranes occurred between 0.1 and 1 MGy. Results emphasize that gamma rays effects on the RO membranes led to the breaking of amide and ester bonds at 1 MGy. These breakings resulted in loss of hydrogen bonds between polyamide chains, and consequently to a relaxation of the polyamide network. Finally, modifications of the polysulfone layer underneath were highlighted. Both relaxation of the polyamide network and modifications of the polysulfone layer could be involved in the drop of the permselectivity properties.