Biochemical indices related with the transformations of C, N and P are frequently used in the diagnosis of soil quality. Such an assessment usually includes analysis of the followin g enzymes – the activity of dehydrogenases and of hydrolytic enzymes such as phosphatases, urease and protease. The objective of the study presented here was evaluation of dairy sewage sludge as an agent causing an improvement of soil quality or its degrad ation. Estimation of soil quality was performed on the basis of a comprehensive study comprising analyses of microbiological and biochemical parameters. The results of the study indicate a stimulating effect of dairy sewage sludge on the soil microorganism s, which was apparent also as an increase in the activity of the enzymes studied. That effect should be attributed to soil enrichment in organic matter, total nitrogen and minerals.