In a two-factor pot experiment impact of two doses of six types of composts prepared from the municipal sewage sludge with an addition of canteen waste, wheat straw and cocoa husk on the total number of bacteria, actinomycetes and fungi in the soil were exmined. The light soil used in the experiment was taken from the Ap level of an arable field. On all the objects with composts there was mineral NPK fertilization applied, the control object was fertilized with the NPK only. The test plant was grass Festulolium which was harvested three times and after the third cut the samples of the soil were taken for microbiological analyses.The conducted research shows that the number of microorganisms in soil was dependent on the dose and the type of the compost. The second dose of the compost, in comparison with the control object, in most composts considerably increased the number of bacteria and the first dose increased the number of actinomycetes. However, the number of fungi, in most cases, with both doses of composts, was lower than in the soil from the control object. The highest number of bacteria was noticed on the object with the co-most prepared from 35% sewage sludge + 35% canteen waste + 30% straw and actinomycetes on the object with the compost prepared from 35% sewage sludge + 35% canteen waste + 30% cocoa husk. The development of the soil fungi was restrained in the highest degree by the first dose of the compost prepared from 35% sewage sludge + 35% canteen waste + 15% straw + 15% cocoa husk and by the second dose of the compost prepared from 70% sewage sludge + 30% straw.