In the paper, the results of studies on changes in the concentration of selected polycyclic aromatic hydrocarbons (PAHs) in the reject water coming from aerobic stabilization of sewage sludge process were given. The sewage sludge samples originating from a treatment of municipal wastewater treatment plant and an industrial coking wastewater treatment plant were investigated. A technological study was conducted using a municipal sewage sludge (control sample) and a mixture of municipal and industrial sewage sludge simultaneously. Aerobic stabilization of sewage sludge process was carried out for 21 days. The concentration of PAHs was determined at the beginning of the experiment (day 0) and in seven-day intervals: after 7, 14 and 21 days. The initial concentration of PAHs in the reject water coming from the municipal sewage sludge was over 44 g/dm3. Industrial sewage sludge was heavily loaded with polycyclic aromatic hydrocarbons. In a reject water of the mixture of municipal and industrial sludge, the initial content of PAHs reached over 5200 g/dm3. During aerobic stabilization of sewage sludge, a decrease in PAHs concentration in reject water was observed. After 21 days of the experiment, the decrease of the sum of analyzed PAHs was in the range of 62–98 %.