Leachate is wastewater containing various pollutants that are harmful not only to the environment, but also to the human being. Current study aims to analyze the efficacy of electric voltage, time, and electrode spacing to obtain optimum mercury (Hg) removal using an electrocoagulation method with iron electrodes. Leachate samples were collected from the TPA Terjun (Medan City, Indonesia). The mercury level in the leachate was 0.04012 at the targeted locations, which was categorized as exceeding the quality standard. Response Surface Methodology (RSM) was used to build models, design experiments, evaluate the effects of independent variables, and determine optimal conditions for mercury removal efficiency. Leachate cannot be decomposed naturally; therefore, certain processing steps are needed to prevent leachate from polluting the environment. Electrocoagulation is an alternative to leachate treatment that can remove heavy metals including mercury (Hg). In this study, the electrocoagulation process was used with iron plate of various voltages (8, 10, 12 volts), distance between electrodes were 1, 2, and 3 cm, and contact time 10, 20, and 30 minutes. To maximize the efficiency of mercury (Hg) removal, data analysis was conducted using RSM. The results showed removal efficiency of 98.862% with recommended voltage, time, and electrode spacing of 12 volts, 29.52 minutes, and 1.111 cm, respectively.