The study was realized in a podzolic soil amended with various doses of sewage sludge i.e. 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%), and subsequently planted with willow (Salix viminalis L.). In the second year of the experiment determinations were made in the soil, of the overall numbers of oligo- and macrotrophic bacteria, filamentous fungi, cellulolytic bacteria and fungi, and “proteolytic” bacteria and fungi. In most cases a stimulating effect of the applied doses of the sludge on the growth of the analysed microbial groups was observed, both in the Ap horizon and in deeper layer of the soil (20–40 cm). The effect was the most pronounced in the surface layer of the soil, but only in relation to the total numbers of oligo- and macrotrophic bacteria, total number of fungi, and number of cellulolytic fungi. The correlations observed in the study between the numbers of particular microbial groups were positive in character.