The research was carried out over three months under laboratory conditions. 3 litre pots were filled with garden soil, crumbled straw, sewage sludge and a biomass of duckweed Lemna minor (obtained from the sewage treatment plant at Chmielnik near Rzeszów) in various combinations. Some pots were filled with Eisenia fetida (Sav). Others were treated like a control, without earthworms. All samples were systematically watered. Common research methods were used to analyze the substrate. Vermicomposting of duckweed in every combinations scentless caused its biotransformation and advantageous changes. Produced vermicompost substrates was characterized by good granular structure. Comparing the substrate types after vermicomposting with their initial state it was noticed the reduction of dry matter content. A tendency was also observed to decreasing organic matter and to increasing the ash content after vermicomposting. The contents of nitrogen, calcium, magnesium and sodium showed a tendency to increase during vermicomposting as compared to those contents from before the experiment. No changes in the content of phosphorus and potassium after vemicomposting were observed.