The study was undertaken to examine feasibility of biological treating of landfill leachate in anaerobic submerged membrane bioreactor. The aim of the work was to estimate the optimal concentration of leachate in the reactor influent and process parameters on the base of anaerobic digestion efficiency. The treatment efficiency under different feeding condition of leachate dilution in the range of 5-75% (v/v) with a synthetic wastewater was studied. A higher COD removal over 95% was maintained with leachate addition of 10% and 20% (v/v). Gradual decrease in organic removals was observed as leachate percentage increase. At leachate addition of 25% the COD removal reached value of 80%. For leachate concentration in influent above 30% (v/v) significant decrease of anaerobic treatment efficiency due to inhibition of microbiological activity was observed. The influence of various hydraulic retention time (HRT) and organic loading rate (OLR) on pollutants removal efficiency and biogas production was also investigated. MBR reactor was operated at HRT in the range of 7-1 days and OLR in the range 0.7-4.9 kg COD/m(3) d. The best anaerobic digestion efficiency (COD removal 90%) was observed for HRT of 2 days and OLR of 2.5 kg COD/m(3) d.