Relevance. The carbon cycle (С) in the soil is closely related to the cycles of nitrogen, sulfur and phosphorus. When soils are contaminated with heavy metals, the functioning of the soil microbiota is disrupted, which affects the biogeochemical cycles of elements occurring in the soil. The authors have studied the activity of enzymes of carbon cycle (C) of Russian soils with different physicochemical properties. Aim. To assess the effect of lead pollution on the activity of enzymes of carbon cycle in ordinary chernozem and sod-podzolic soil. Objects. In a laboratory model experiment, the activities of two types of soils were studied: ordinary chernozem and sod-podzolic soil. Soils contaminated with lead (Pb) at doses of 100, 1000 and 10000 mg/kg were incubated under constant conditions (soil moisture and air temperature) for 30 days. At the end of the experiment, each variant of each soil type was dried, and the enzymatic activity was determined in 3–6 replicates. Methods. The authors studied the activity of eight enzymes of the oxidoreductase and hydrolase classes of carbon cycle: dehydrogenase, peroxidase, polyphenol oxidase, glucose oxidase, invertase, β-glucosidase, cellulase, chitinase. As a result of determining the enzyme activity, the integral index of soil enzymatic activity was estimated. Results. Cellulase and chitinase of sod-podzolic soil were stimulated at the lowest concentration – 100 mg Pb/kg soil. Enzymes of the oxidoreductase class are more sensitive than hydrolases, but hydrolases are more informative than oxidoreductases. Cellulase is the most sensitive and informative enzyme in sod-podzolic soil contaminated with lead. For ordinary chernozem, the most sensitive enzyme is glucose oxidase, and the most informative is invertase. Invertase has the greatest informativeness for all enzyme activity classes in ordinary chernozem, and cellulase and β-glucosidase have it in sod-podzolic soil. Glucose oxidase has the greatest sensitivity for all enzyme activity classes in ordinary chernozem, and peroxidase has it in sod-podzolic soil. The results of the study can be used in enzymatic diagnostics of the state of soils after contamination with heavy metals.