The complex formation of Cr(III), Fe(III), Co(II), Ni(II), Cul(II), and Zn(II) ions with partially phosphorylated poly(vinyl alcohol) (P-PVA) in aqueous solution is studied by means of potentiometric titration and electronic as well as e.s.r. spectroscopy. The titration data and spectroscopic results suggest that bivalent and trivalent metal ions bind with two and three phosphoric acid groups in P-PVA at pH <3.5, respectively. Overall formation constants, log K, for the bivalent metal ion and P-PVA are about 4.6. The electronic and e.s.r. spectroscopic results indicate that cupric ion forms a polynuclear complex of Cu(OH)(2) solubilized by unreacted hydroxyl groups in P-PVA at pH >6.2.