In this study, the treatment of landfill leachate in supercritical water conditions with and without catalyst use was investigated. A real waste, namely lathe waste, was used as the catalyst. The experiments were made at a constant 25 MPa pressure, at four reaction temperatures in the range of 450-600C and four reaction times between 60 and 150 s. Through the experiments, the impacts of reaction temperature, reaction time and the use of lathe waste catalyst on landfill leachate treatment were investigated. The efficiency of the treatment was evaluated in terms of liquid reaction products’ total organic carbon (TOC) and total nitrogen (TN) conversions. As a result, it was seen that elevated reaction temperatures and long residence times favored TOC conversions. On the contrary, greater TN reductions were encountered at lower reaction temperatures. The use of lathe waste was observed to promote the treatment efficiency for all experimental runs. The highest TOC conversion was seen at 600C and 150 s conditions, which was 57.2% for the noncatalytic treatment. The employment of lathe waste improved this value to 66.9%. As for TN, the highest conversion was encountered at 450C and at a reaction time of 150 s. At the foresaid reaction conditions, using lathe waste as the catalyst provided 41.9% reduction in the TN content of landfill leachate.