Water-soluble Cu(II) complexes of poly-4-vinylpyridine, partially quaternized by methyl bromide or dimethylsulphate (PP~Mt), and of the analogue (4-ethylpyridine) were studied by physicochemical technique such as visible spectrophotometry, viscosity, speed sedimentation and EPR spectroscopy. Peculiarities of the complex formation reaction were observed for the polymer compared to the analogue. The predominant formation of tetrapyridinate-Cu(II) species [(CuL4)] 2 Γ· was found to take place in aqueous solution for PPrMt with degree of quaternization (fl) 20,24,37,49,57,65 per cent over a wide range of icy/ Cu(II) molar ratios. In addition, not all the free polymer pyridine residues are capable of forming [Cu L4] 2 + complexes even though there is a large excess of Cu(ll) ions. The maximum value of the pyridine fraction forming [Cu L4] 2+ in PPrMt-20, 24, 37, 49 (obtained by spectroscopic titration) was found to be 45-50 per cent. Addition of Cu(NO3)2 to the aqueous polymer solution causes strong reduction of specific viscosity and increase of sedimentation coefficient from ~ 1 S to ~ 6 S. These data lend to the suggestion of the existence of macromolecular associates bound by Cu(lI) ions and approximate estimation of their average molecular weight. It was shown also that Bjerrum's procedure cannotbe used to account for the polymer stability constants. The differences between complex formation for polymer pyridine and monomer pyridine seem to be due to the high local pyridine concentration in the coil of the macromolecule and the hydration effects of the polymer chain on the characteristics of the pyridine residues.