Up flow anaerobic sludge blanket (UASB) treatment has proved its efficiency among other treatment methods especially for hardly degradable wastewaters such as industrial wastewaters and leachate. UASB is a widely used reactor with a resistance biomass. Waste landfills' leachate is one of the most polluted wastewaters which cause great concerns due to landfill implementations for municipal solid waste management. One of its impacts is affecting underground and surface waters. Always major tasks are done to improve leachate quality and minimize its quantity by controlling landfill influents (waste and water) and effluents (gas and leachate) but leachate generation is inevitable and large areas of soil and water can get polluted by a small amount of that. Thus, regarding these issues, legislations are going to get stricter so has made leachate treatment compulsory.A UASB pilot plant was established to examine the effects of different parameters on the anaerobic treatment of municipal solid waste (MSW) leachate in both batch and continuous operation. The pilot plant was designed based on the ability of the selected system and normal organic loading rate (OLR) using diluted leachate from Tehran's solid waste landfill. In the first stage (Batch operation), different COD concentrations from 1200 up to 6443 mg/l and Organic Loading Rate (OLR) of 1.36 to 6.6 kg COD/m3.d and Hydraulic Retention Time (HRT) of up to 21.6 hours were examined. In continuous operation, inlet COD and OLR were increased up to 25960 mg/l and 30kg COD/m3.d respectively. Results show that there is 90% efficiency in COD removal for batch situation where OLR is 4.48 kg COD/m3.d and inlet COD is 4000 mg/l. In continuous regime with OLR of 22.6 kg COD/m3.d and COD of 20000 mg/l and 21.2 hours of HRT and 38.8 hours of circulation, COD removal efficiency was raised up to 63.5%.