The article presents evaluation of effectiveness of sewage treatment by the Tarnow Group Sewage Treatment Plant. On the basis of the results of raw and treated sewage physico-chemical analyses, the effectiveness of decreasing the cho-sen sewage pollutants was evaluated. The following pollutants’ indexes were tested: BOD5, COD, total suspended solids, general nitrogen and general phosphorus. The research period was from January 2006 until November 2007. The paper presents the amount of transgressions of each index in relation to the admissible values from the water-law permission. Basing on the performed analy-sis the following effectiveness of the pollutants’ removal was evaluated: BOD 98,9%, COD 92,9%, total suspended solids 95,1%, general nitrogen 91,3%, gen-eral phosphorus 87,4%. The tested sewage treatment plant may be certified to op-erate in high quality and the sewage treated by this plant doesn’t threaten the col-lector of the treated sewage.