In this study, a trichloroethylene (TCE)-spill site was selected to assess the feasibility of enhanced in situ anaerobic bioremediation of TCE-contaminated groundwater using hydrogen as the electron donor produced from nanoscale zero-valent iron (nZVI). Results of hydrogen production experiments show that nZVI had a good efficiency on hydrogen production. Results of microcosm study show that indigenous microorganisms were capable of degrading TCE under anaerobic reductive dechlorinating conditions. Compared to the live control and autoclaved control microcosms, microcosms with hydrogen addition significantly enhanced the TCE removal rates. Results imply that nZVI can be applied as the source of hydrogen to bioremediate TCE-contaminated groundwater under anaerobic conditions. Except for the biotic mechanism, the supplied nZVI can also cause the TCE degradation via abiotic mechanism through oxidation-reduction process. For field application, if proper doses of iron nanoparticles can be applied in the mid- or downgradient areas, both chemical and biological mechanisms can enhance the removal of the contaminants and their byproducts. Knowledge and comprehension obtained in this study will be helpful in designing an enhanced in situ anaerobic bioremediation system for a TCE-contaminated site. The nZVI treatment scheme would be expected to provide a more cost-effective alternative to remediate chlorinated-solvent contaminated aquifers.