The Fenton's process was evaluated for mature leachate treatment, after the biological one, by means of an experimental design divided into three steps: analyzes of the factors separately to establish values ranges; evaluation of significant factors and their interactions by a fractional factorial design; and analyzes of factors by a Central Composite Design (CCD). Performance results were measured by removal efficiency of the chemical organic demand (COD) and color. Four factors were considered: [H2O2], [H2O2]/[Fe2+], pH, and addition mode of reagents. The removal achieved were 88 (COD) and 99% (color) for: [H2O2] = 480 mM (6.02 mg H2O2 mgCOD -1 ); [H2O2]/[Fe 2+ ] =6 (1.65 mg Fe 2+ mgCOD -1 ); pH=3.5, and reagents dosages divided into three stages. For the range evaluated, the [H2O2] had the greatest influence in the COD and color removal. The models established for COD and color removal were able to explain 86.7 and 80.3% of the variance around the average. Alkalinity concentration and the characteristics of the leachate used may interfere in the Fenton efficiency, so should be the focus of further research. The addition of the reagents shared in fractions was not significant in the treatment, however, it is recommended for system operation, avoiding foam formation. In the biological treatment for nitrogen removal from landfill leachate, there is high alkalinity consumption, therefore, when one used before Fenton's process, it helps to reduce the pH. This and the possibility of applying Fenton's process at circum-neutral

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