In this study, magnetic Pd/Fe nanoparticles were synthesized using nanoscale Fe3O4 (nFe(3)O(4)) and nanoscale zero-valent iron (nZVI) to significantly enhanced 2,4-DCP dechlorination. nFe(3)O(4) was found to restrain the formation of passivated layer on nZVI surface and promoted the electron transfer. Earlier, only 35.8% 2,4-DCP (C-initial = 20 mg L-1) was removed by 3.0 g L-1 Pd/Fe nanoparticles, whereas it remarkably increased to 76.4% by magnetic nanocomposites (2.0 g L-1 nFe(3)O(4) and 3.0 g L-1 Pd/Fe). A satisfactory long-term stability of nFe(3)O(4)-Pd/Fe was exhibited and the 2,4-DCP removal efficiency reached to 100%, 100%, 93.5%, 93.0%, and 90.1% in five consecutive cycles, respectively. Moreover, the nanocomposites were easily separated from the solution after reaction and that reduced environment related risks of nanoparticles. Weak acidic condition was considered feasible for 2,4-DCP dechlorination. Negative co-precipitation occurred on nFe(3)O(4)-Pd/Fe surface in the presence of common dissolved anions (such as Cl-, PO43-, and HCO3-) and humic acid (HA). The 2,4-DCP dechlorination was notably accelerated by dissolved metallic ions (Fe2+, Cu2+, and Ni2+), and 2,4-DCP was completely removed in 5 h reaction time. The application of nFe(3)O(4)-Pd/Fe nanocomposites could be highly effective for an in situ pollutants remediation measures. (C) 2013 Elsevier B.V. All rights reserved.