The reaction of -CH3 free radicals with Cun(NH2CH2CO2)2 in aqueous solutions was studied. The formation of the unstable intermediate (NH2CH2CO2)2Culn-CH3(aq) in this reaction was observed. This intermediate decomposes into Cu111-(NH2CH2CO2)2+(aq) + CH4. The formation of Cum(NH2CH2COf)2+(aq) is not observed, as this complex is short-lived under these conditions and decomposes via ligand oxidation. The *CH3 free radicals react with the transient complex (NH2CH2CO2)2Cum-CH3(aq) to form ethane and CuM(NH2CH2COf)2; the specific rate of this reaction approaches the diffusion-controlled limit. The results thus point out that aliphatic free radicals can oxidize copper(Il) complexes to copper(HI) complexes. The results suggest that the reactions of aliphatic free radicals with copper complexes might cause the reported radiosensitization by copper compounds.