Results of analyses of underground waters on a municipal landfill site conducted in 2004-2008, prior to leachate cleaning were presented and discussed in the paper. The sewage quality analysis comprised pH, electrolytic conductivity, TOC, Cr+6, Pb, Cd, Cu, Hg, Zn and PAHs. Results of leachate water testing were compared with standard values and subjected to comparative analysis taking into consideration also atmospheric precipitation amount. The aim of the paper was to assess the leachate water quality in conditions of exploited municipal landfill. The analyzed waters were characterized by variability of composition evidenced by increasing pH values, electrolytic conductivity and heavy metal concentrations (Cr, Hg) total organic carbon (TOC) and PAHs, but also by a decline in heavy metal contents (Pb, Cd, Cu and Zn).