In the presented work, relations between activity of dehydrogenase and the content of polycyclic aromatic hydrocarbons in light soil fertilised with sewage sludge was studied. Sewage sludge was introduced to the soil in the following doses: 30 Mg/ha, 75 Mg/ha, 150 Mg/ha, 300 Mg/ha and 600 Mg/ha. The content of PAI-ls in sewage sludge-amended soil was proportional to sewage sludge dose. Soil fertilisation with sewage sludge stimulated the activity of the dehydrogenase enzymes. With passing of time, a gradual decrease in the activity of dehydrogenase was observed. The coefficients of correlation between activity of the enzyme and PAH content showed that an addition of sewage sludge (with PAI-I content of 5712 μg/kg) had a stimulating effect on dehydrogenase activity in doses of 75 and 150 Mg/ha.