Potentilla reptans L. belongs to the least studied of the plants from Rosaceae family, Potentilla genus. There are no data on cytotoxicity of P. reptans extracts, though traditionaly it was used as antiinflammatory and antiinfective. The aim of these studies was to investigate potential antitumor activity of aqueous extracts (rhizome and aerial parts) of P. reptans on 4T1 mouse breast cancer cell line. _Aqueous extracts of rhizome and aerial parts of P. reptans were tested for cytotoxicity by the MTT colorimetric assay on 4T1 cancer cell line in concentration range 100-800 microg/mL. Aqueous extracts of P. reptans rhizome and aerial parts show concentration dependent cytotoxic effect in the range of tested concentrations. ICE50 value of P. reptans rhizome extract was 280.51 +/- 1.16 microg/mL. IC50 value of P. reptans aerial parts extract was 310.79 +/- 1.22 microg/mL. The significant difference in cytotoxicity among tested concentrations was observed. Aqueous extracts of P. reptans rhizome and aerial parts demonstrated weak cytotoxic activity on 4T1 mouse breast cancer cell line, which is in correlation with current cytotoxicity data for aqueous herbal extracts. Rhizome extract of P. reptans has slightly higher antitumor activity than aerial parts extract. The results represent the first report on cytotoxicity for this plant and further research on human cell lines is indicated.