In the present study the potential of the earthworm Eisenia andrei to modify chemical and microbiological properties, with a special focus on the nutrient content of fresh organic matter, was evaluated during 16 weeks of vermicomposting of cattle manure and sewage sludge. Samples were periodically collected in order to determine the changes in inorganic nitrogen (N), in total microbial biomass and activity, as well as in the total and available content of macro- and micronutrients. An optimal moisture level, ranging from 75% to 88%, was maintained throughout the process. The content of organic matter decreased over time, but no changes were found in this parameter as a result of earthworm activity. The carbon/N ratio rapidly decreased, but only in the manure, reflecting rapid decomposition and mineralisation of the organic matter by the earthworms. An increase in N mineralisation was also attributable to the presence of earthworms, although in the manure this effect was hardly detectable before the eighth week of vermicomposting. Earthworm activity also enhanced the total content of potassium, calcium and iron together with an increase in the availability of phosphorus and zinc. We did not detect a significant earthworm effect on microbial respiration, but their activity increased greatly microbial biomass nitrogen in sewage sludge.