In this study, cobalt-60 gamma radiation was used to degrade 2,4-dichlorophenoxyacetic acid herbicide (2,4-D) in methanol in the presence of humic acid. The 2,4-D solution was irradiated with different doses. The herbicide was completely degraded after treatment with a dose of 150 kGy. The influence of humic acids was verify in higher doses (75 and 100 kGy) only. ESI/MS and MS/MS identified 3-chlorophenol as the intermediate product. The radiolytic yield (G) of 2,4-D degradation was calculated.