This study was to investigate the reaction behavior of nanoscale [Fe3O4]MgO and trichlorothylene (TCE) in aqueous solutions. In addition, effects of environmental variables on TCE removal from a simulated groundwater system were investigated. At first, two types of metal oxide composites containing both nanoscale Fe3O4 and MgO (designated H-[Fe3O4]MgO and S-[Fe3O4]MgO, respectively) were prepared. Then they were characterized and verified by various apparatuses and methods including X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, specific surface area measurements. Since the substrate of S-[Fe3O4]MgO with a molar ratio of Fe3O4/MgO = 1/5 (designated S1/5-[Fe3O4]MgO) had a much greater specific surface area than that of the substrate of S-[Fe3O4]MgO with a molar ratio of Fe3O4/MgO = 5/5 (designated S5/5-[Fe3O4]MgO), S1/5-[Fe3O4]MgO was selected as the model composite for the treatment of TCE in this study. Results of batch tests showed that S1/5-[Fe3O4]MgO had the best treatment performance among various metal oxides and their composites. For an initial TCE concentration of 10 mg/L, however, only 45% removal could be achieved by 5.0 g/L of dispersed S1/5-[Fe3O4]MgO. Nevertheless, a greater removal efficiency could be obtained for a higher initial TCE concentration in a simulated groundwater system. Test results also showed that a lower temperature and higher pH would retard the relevant reaction rates in TCE removal. In the simulated groundwater system employed in this work, the existence of humic acid (< 10 mg/L) played an insignificant role in affecting the TCE removal. Analysis of TCE adsorption on S1/5-[Fe3O4]MgO in aqueous solution indicated that a Langmuir-type of chemical adsorption would have a better fit. Results of gas chromatography further showed the existence of small to trace amounts of TCE degradation products including cis-1,2-dichloroethylene, trans-1,2-dichloroethylene, vinyl chloride, ethene and methane, etc. Thus, the relevant reaction mechanisms and pathways for the destructive adsorption were proposed.