The antioxidant (DPPH, superoxide anion radical scavenging and FRAP) and antiproliferative activities against Vero cells (african green monkey kidney), C6 cells (rat brain tumor cells) and HeLa cells (human uterus carcinoma) of Cirsium arvense (CA) of all parts [root (Kinghorn et al. 2004), stem (CAS), flower (CAF) and leaves] and isolated compounds were investigated in vitro. CAR was shown to have the highest antiproliferative activity against HeLa and C6 cell lines as compared to other parts. A flavon glucoside (linarin), a steroid glucoside (daucosterin), a steroid (stigmasterol) and a new benzymidazole molecule (E26-(3-(5,6-dimethoxy-1H-benzo[d]imidazol-2-yl) allyloxy) 25-(hydroxymethyl)-tetrahydro-2H-pyran-2,3,4triol) were isolated from the CAR. The structures of these molecules were determined by the C-13 (carbon) and H-1 (proton)-Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared Spectroscopy (FT-IR), and Gas Chromatography-Mass Spectrometry (GC-MS) techniques. CAR for C6 cell line, CAS for HeLa and Vero cell line were observed the highest antiproliferative activity. In addition, CAR showed the stronger DPPH activity than a-tocopherol and BHTat high concentrations. The FRAP and superoxide anion radical scavenging activities of CAR (Fr-7) were found to be higher than BHT.