Factors affecting the reduction of nitroaromatics by zero-valent iron in groundwater were investigated by using 2,4-dinitrotoluene, nitrobenzene, and 2,4,6-trinitrotoluene. Batch experiments showed that the ratio of adsorbed nitrobenzene to cast iron surface area was approximately 30%, similar to those of 2,4-dinitrotoluene and 2,4,6-trinitrotoluene. Dissolved chloride (0.1 mM) and sulfate ions (0.01 mM) could enhance the reduction of 2,4-dinitrotoluene by zero-valent iron via the enhancement of iron corrosion. Long-term column experiments showed the iron consumption in the column to be attributable to the reduction of 2,4-dinitrotoluene in groundwater. Therefore, the longevity of the iron column may be predicted stoichiometrically by the amount of 2,4-dinitrotoluene in groundwater. The use of Ottawa sand in the iron column did not result in a significant clogging problem during 2,4,6-trinitrotoluene reduction under the specified conditions. However, the use of either silica sand or a high concentration of dissolved bicarbonate/carbonate in solutions was shown to effect clogging of the iron column. The results suggest that some important factors should be considered when applying an iron reduction process for the treatment of nitroaromatics in groundwater.