In this study, the Fenton process was found to be successful to treat landfill leachate rejected after reverses osmose treatment. Central composite design (CCD) and response surface method (RSM) were applied to evaluate and optimize the interactive effects of three operating variables, initial pH and dosages of H2O2 and Fe2+ on physical and oxidative performances of Fenton process. Six dependent parameters such as overall chemical oxygen demand (COD) removal, COD removals of oxidation and coagulation, mineralization, humic substances (HS) removal and sludge volume ratio (SVR) were either directly measured or calculated as responses. According to analysis of variances (ANOVA) results, six proposed models could be used to navigate the design space with high regression coefficient R-2 varied from 0.9489 to 0.9988. It was found that initial pH. H2O2 and Fe2+ dosage had significant effects on the overall COD removal, mineralization and HS removal due to their respective effects on the oxidation and coagulation removals. Synergies effect of oxidation and coagulation during Fenton process controlled the treatment. The visual search of overlaying critical response contours plot was demonstrated. The results indicated the optimum conditions to be 3.64 of initial pH, 100 mM of Fe2+ and 240 mM of H2O2 dosage, respectively. The experimental data and model predictions agreed well. The overall COD removal, COD removals of oxidation and coagulation, mineralization, HS removal and SVR of 71.81%, 46.22%. 25.80%, 63.81%, 91.53% and 3.50 ml/mM were demonstrated. (C) 2010 Elsevier B.V. All rights reserved.