To investigate the influence of radiolysis on kinetics and factors of dimethyl phthalate(DMP), the aqueous DMP solution is degraded by 1.8 MeV E-beam, following pseudo-first-order kinetics. The rate constant of DMP degradation decreased exponentially with increasing initial DMP concentration. The DMP is favorably degraded by radical scavengers under its low concentration and alkaline condition. At high doses, the DMP is attacked by e_aq^– and ·OH, producing monomethyl phthalate, phthalate acid, and a series of aliphatic carboxylic acids, which are completely mineralized into H₂O and CO₂.