The paper presents the compositional analysis of sewage supplied to and discharged from the wastewater treatment plant in Kolbuszowa Dolna in the Subcarpathian region. The analysis was based on three basic indicators of sewage pollution (BOD₅, COD_Cr, total suspended solids) and two biogenic indicators (total nitrogen and total phosphorus). The composition of sewage was studied in the years 2010–2015. Basic descriptive statistics for the values of the analyzed indicators of sewage pollution were summarized and the obtained results were interpreted. The study showed that the sewage was susceptible to biological treatment. Descriptive statistics for the relationship between the following indicators were presented: COD_Cr/BOD₅, BOD₅/N_tot, BOD₅/P_tot. The collected results indicate high variability of the composition of sewage entering the studied facility. The coefficients of variation for the values of basic indicators (BOD₅, COD_Cr, total suspended solids) in the raw sewage were similar and amounted to W_n = 0.45 while for total nitrogen it was W_n = 0.33 and for total phosphorus W_n = 0.40. The analysis of the collected material showed that sewage entering the treatment plant was readily biodegradable. On the other hand, the treated sewage was characterized by low values of the analyzed indicators, much below the permissible values provided by the water permit. The raw sewage was divided into five groups depending on the concentration of each pollution indicator. The number of raw sewage samples was determined for each group of the analyzed pollution indicator concentrations.