Leachate is known to be hazardous wastewater in terms of its organic matter and ammonia content. Various methods have been studied extensively for the treatment of different types of leachate. However, scheduled waste leachate is rarely studied due to its complex characteristics and highly contaminated nature compared to other types of landfill leachates. In this study, hydrated lime (Ca(OH)2) and caustic soda (NaOH) as softener agent were used for increasing the pH of the treatment process of scheduled waste leachate to remove ammonia-nitrogen (NH3-N). Chemical oxygen demand (COD) and colour removal were also evaluated. Jar test experiments was performed using Ca(OH)2 and NaOH at varying dosages ranging from nil to 12 g L-1. A Historical Data Design (HDD) of Response Surface Methodology (RSM) was employed to optimize the parameters affecting NH3-N, COD and colour removal efficiency. The optimal conditions obtained from desirable response were predicted at 5.9 g L-1 of Ca(OH)2 dosage, where the maximum NH3-N, COD and colour removal efficiency would be 49%, 18% and 66%, respectively. Meanwhile for NaOH, dosage of 6.4 g L-1 was predicted to remove NH3-N, COD and colour up to 32%, 4% and 42%, respectively. The predicted values concurred with the experiments, in which Ca(OH)2 successfully reducing NH3-N, COD and colour up to 52 %, 17.5 % and 65 %, while NaOH could only remove NH3-N, COD and colour by up to 35 %, 2 % and 49 %, respectively. The results obtained from this study suggest that hydrated lime (Ca(OH)2), is more feasible to be used for the pre-treatment process of scheduled waste leachate as less dosage is required with higher removal efficiencies of NH3-N, COD and colour. This study demonstrates that RSM was a reliable tool to predict the optimum dosage and suitable types of chemicals for the removal of NH3-N, COD and colour from the available data.