Subcolloidal (<0.1 mu m) iron-silver (1% Ag) particles were synthesized for the transformation of chlorinated benzenes in aqueous solution. Hexachlorobenzene (HCB) (4 mg/L) was dechlorinated to tetra-, tri-, and dichlorobenzenes (TeCB, TCB, and DCB, respectively) within 24 h at a metal loading of 25 g/L. Principal degradation products included 1,2,4,5-TeCB, 1,2,4-TCB, and 1,4-DCB. Continuous dechlorination was observed during a 57-day experiment. The rate of dechlorination was positively correlated to the silver loading of the bimetallic particles. The bimetallic particles also effectively degraded penta- and tetrachlorobenzenes (PCB and TeCB, respectively). The Fe/Ag particles could become a cost-effective alternative to the previously reported Pd/Fe particles. The subcolloidal bimetallic particles may be applied in slurry reactors, in situ applications, and in combination with biological treatment for the complete degradation of chlorinated benzenes and PCBs.