The aim of the present study was to compare the effect of sulfated fucopolysaccharides isolated from Fucus vesiculosus on cell lines HeLa G-63, Hep G2 and Chang liver. Native fucoidan F3 and two fractions (F3-0.5 and F3-1), obtained by anion-exchange chromatography, were analyzed using chemical methods and IR-spectroscopy. Their action on cells demonstrates that F3 and F3-1, characterized by higher content of sulfates, preferable location of sulfo-groups at C4 atom of fucose residue and low content of uronic acids, inhibit cell proliferation more efficiently. Human liver tumor cells Hep G2 appeared to be the most sensitive to fucoidan treatment whereas nonmalignant human cells Chang liver were the least sensitive.