The main objective of this work was to evaluate an effectiveness of removing organic and inorganic pollutants from landfill leachate in a long-term reverse osmosis (RO) study. Investigations were carried out during the first year of RO exploitation since February till September 2013. Over 20 parameters were analysed both in leachate and permeate samples. In the first 1-year operation, the treatment performance was feasible for most of analysed leachate pollutants. The average removal rate of chemical oxygen demand (COD), electro-conductivity, ammonia nitrogen (N-NH4 +), total inorganic nitrogen, cyanides (CN−), iron (Fe) and chlorides (Cl−) reached 97, 97.2, 98.7, 99, 93, 97.6 and 98 %, respectively. A smaller reduction rate—of 83 and 86 %—was obtained for sulphates (SO4 2−) and sulphides (S−), what is the result of sulphuric acid addition before treatment process in order to decline a pH to a value of 6.0–6.5. Boron was eliminated only by 81 % due to easy transportation through the membrane uncharged species of boric acid B(OH)3, which predominate in leachate. Average reduction of nitrites (NO2 −) and nitrates (NO3 −) was 63.8 %, which is the result of inhibition NO2 − oxidizers by nitrous acid and relatively low ratio of biochemical oxygen demand and COD (BOD/COD). The obtained permeate quality does not meet the Polish discharge standards for S−. It is also foreseen that the concentration of N-NH4 + in maturate leachate will increase in the next years.