Our study was conducted on a podzolic soil from a field experiment, fertilized with increasing doses of fermented municipal-industrial sewage sludge: 30 Mg·ha^-1 (1%), 75 Mg·ha^-1 (2.5%), 150 Mg·ha^-1 (5%), 300 Mg·ha^-1 (10%) and 600 Mg·ha^-1 (20%). Following the preparation as above, the soil was planted with basket willow (Salix viminalis L.). After five years of maintaining the plantation in Ap horizon of the soil, continued stimulation was observed in the growth of most of the microbial groups under study, i.e. oligo- and macro- trophic bacteria, filamentous fungi, cellulolytic bacteria and fungi, and a slight increase in the numbers of proteolytic bacteria. A certain intensification was also observed in the respiratory activity, rate of cellulose mineralization, nitrification, dehydrogenase and proteolytic activity. The process of ammonification, on the other hand, was subject to inhibition. In the deeper layer of the soil (20-40 cm) a positive effect of the sewage sludge was also observed, but it was notably weaker and related to only some of the aforementioned parameters (macrotrophic bacteria, filamentous fungi, cellulolytic bacteria, respiration, and rate of cellulose mineralization).