The study was carried out on two peaty-muck soils at different states of secondary transformation. The main purpose of the study was to examine the relations between some physicochemical and surface properties of muck soils and their biological activity. The total number of microorganisms and their respiration activity were determined. The effectiveness of utilization of carbon substances from the soil by the bacteria increased with progressing transformation state of the peaty-muck soils. Organic carbon content in the soil decreased distinctly at the higher stages of secondary transformation and that influenced the quantity and activity of soil microorganisms. At the same time, the surface charge was more developed in the soil at the higher stage of transformation. Moreover, under given soil conditions, active places in soil were immobilized by charge-possessing bacteria. The process of secondary transformation influenced the soil environment for the microbes by changing the physicochemical and surface properties of the soil, and therefore influenced the number of micro-organisms and caused changes in the biological activity in the soils.