Interactions between poly(maleic anhydride-alt-acrylic acid), [poly(MA-alt-AA)] and Cu2+, Ni2+, and Cd2+ ions were studied by UV-vis spectroscopy and viscosimetry. Effects of nature and the concentrations of the metal ions on the complex formation were investigated and the formation constants of each complex were determined by the mole-ratio method. UV-vis studies showed that the complex formation tendency increased in the followed order: Cd(II) < Ni(II) < Cu(II). This order was confirmed by the Irving-William series and the Pearson's classification. The influence of metal ions on the reduced viscosity of poly(MA-alt-AA) increased in the following order: Cu(II) < Ni(II) < Cd(II), and this result was explained by the concentration effect. (C) 2004 Wiley Periodicals, Inc.