To identify the decomposition characteristics of trimethylamine (TMA) by electron beam (EB), we conducted an experiment based on process parameters, including absorbed dose (2.5-10 kGy), background gas (air, O-2, N-2 and He), water content (1,200, 14,300, and 27,500 ppm), initial concentration (50, 100, and 200 ppm) and reactor type (batch or continuous flow system). Air background gas showed a maximum TMA removal efficiency of 86 % at 10 kGy and that was the highest efficiency of all background gases. Energy efficiencies were higher when the absorbed dose was lower (e.g., 2.5 kGy). Decomposition efficiencies of all initial TMA concentrations were approximately > 90 % at 10 kGy. Removal efficiencies increased up to 30 % as water vapor increased. As a by-product, it is observed that CH3 radical formed by EB irradiation was converted into CH4 by reaction with residual TMA, (CH3)(2)NH, and H. These results suggest that EB technology can be applied for TMA treatment under low concentration and high flow rate conditions.