Complex formation between polymethacrylic (PMAA) and polyacrylic acids, and star-shaped poly(ethylene glycol) prepared by ethoxylation of pyrogallol (Pyr-PEG) has been studied viscometrically and by potentiometric titration in water solution. The competitive ability of Pyr-PEG and of the derivatives of the ethoxylation of phenol and hydroquinone in complex formation with PMAA has been compared by UV spectroscopy. Pyr-PEG turns out to be the weakest competitor because of its chemical structure.