Degradation of the insecticide O,O-diethyl O-3,5,6- trichloro-2-pyridyl phosphorothioate (chlorpyrifos) in aqueous solution was investigated using iron salts and potassium persulfate during ZVI treatment through a series of batch experiments. The degradation rate of chlorpyrifos increased with increases in the concentrations of iron salts and potassium persulfate in the aqueous system. Ferric chloride was found to be the most effective iron salt for the ZVI-mediated degradation of chlorpyrifos in aqueous solution. Further, the iron salts tested could be arranged in the following order in terms of their effectiveness: FeCl₃> Fe₂(SO₄)₃>Fe(NO₃)₃. The persulfate-ZVI system could significantly degrade chlorpyrifos present in the aqueous medium. This revealed that chlorpyrifos degradation by treatment with Fe⁰ was promoted on adding ferric chloride and potassium persulfate. The kinetics of the degradation of chlorpyrifos by persulfate-amended Fe⁰ was higher than that for iron-salt-amended Fe⁰. This suggests that using a sequential Fe⁰ reduction-ferric chloride or Fe⁰ reduction-persulfate process may be an effective strategy to enhance the removal of chlorpyrifos in contaminated water.