Chemical cleaning of iron pipes and boilers generates complex wastewater so-called derusting wastewater containing high concentrations of organic chelating agents such as ethylenediamine tetraacetic acid (EDTA) and metals, primarily iron.  Complex wastewater makes it difficult to be treated by conventional methods due to metal complexation.  However, both the organic chelating agents and the metals in derusting wastewater must be removed.  This study investigated the use of Fenton reaction followed by hydroxide precipitation for this type of industrial wastewater treatment.  The optimum conditions including initial pH, hydrogen peroxide (H₂O₂) to ferrous iron (Fe²⁺) molar ratio (H₂O₂: Fe²⁺), and precipitation pH were also determined in a Jar Test apparatus at the room temperature.  The results indicated that removal efficiencies of total chemical oxidation demand (total COD) and iron depended on initial pH, H₂O₂: Fe²⁺ molar ratio, and precipitation pH.  At the optimum initial pH of 3.0, the H₂O₂: Fe²⁺ molar ratio of 40:1, and the precipitation pH of 9.0, the removal efficiencies of total COD and total iron were as high as 90% and 94.4 %, respectively, after 20 min of reaction time.  It was found that total COD was removed by Fenton reaction while precipitation was responsible for the total iron removal.  In summary, Fenton reaction with subsequent hydroxide precipitation can be feasibly applied for the removals of total COD and total iron from the complex derustiong wastewater.