Reversed-phase HPLC determination of the herbicide MCPA and its products of radiolytic degradation has been optimized. The radiolytic degradation was carried out using gamma-irradiation and was optimized in terms of irradiation dose and pH of irradiated MCPA solution. Decomposition of 100 ppm MCPA in pure solutions required irradiation with a 3 kGy dose. The main products of irradiation in the dose range up to 10-kGy were various phenolic compounds and carboxylic acids. The developed method was applied for treatment of industrial waste from production of MCPA. The 10-kGy dose was needed for decomposition of 500 ppm of MCPA in the industrial waste samples; however, the presence of stoichiometric amount of hydrogen peroxide in the irradiated waste allowed a 50% reduction of the gamma-irradiation dose. Despite complete decomposition of MCPA in the industrial waste, in order to reduce the toxicity of irradiated waste, measured by the Microtox bioluminescence test, higher than a 10 kGy irradiation dose was needed.