Introduction. Glioblastoma is one of the most aggressive malignant tumours of the central nervous system. Current therapies are not efficient enough to cure the disease. Thus, the identification of new substances with anti-glioblastoma potential, including those of natural origin such as Taraxacum officinale, is of utmost importance. The objective of the studywas to evaluate the action of Taraxacum officinale FH Wigg (TO) extracts on glioblastoma cell line U-251 MG viability, correlated to total phenolic content (TPC) of the extracts. Material and methods.TO leaf and root extracts were prepared with dimethyl sulfoxide (DMSO) and ethanol of different concentrations (20%, 50% and 80%). Glioblastoma U-251 MG cells viability was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide test (MTT). The TPC was determined spectrophotometrically by Folin-Ciocalteu method. Results.The highest antitumour activity (36.6±4.92%) was identified in case of TO leaves extracts made in ethanol of 50% (150,000 μg/L), as well as in case of leaves (44.98±5.21%) and roots (48.61±3.89%) extracts made with alcohol of 80% (respectively, 50,000 μg/L and 40,000 μg/L). The lowest antitumour activity (97.4±1.69%) was determined in case of roots extracts made with DMSO (1.86 μg/L). The TPC content varied from 2 to 38 mg TAE/mL. The maximum content of phenolic compounds was found in leaves extracted with ethanol. The increase of TPC content correlated with the decrease in the viability of tumour cells. Conclusions.The extracts of Taraxacum officinale exhibit inhibitory effects on the viability of glioblastoma cells. The actions carried out depend on the type of extractant, its concentration, the part of the plant and the total content of phenols.