The kinetic analysis and the characterization of copolymer systems at high conversion based on the free radical polymerization of N-vinylpyrrolidone, VP, and 2-hydroxyethyl methacrylate, HEMA, is analyzed on the basis of the reactivity ratios of these monomers as obtained by the Tidwell and Mortimer nonlinear method. Characterization of copolymers prepared at different conversion degrees was carried out by using micellar electrokinetic chromatography, MEKC, as well as by size exclusion chromatography, SEC. The experimental results obtained demonstrate a noticeable change of the composition of copolymer chains with the conversion degree and a good agreement between the approximation of the Skeist's kinetic treatment and the experimental data. Both MEKC and SEC provide valuable complementary information with respect to the average composition of copolymer chains and their macromolecular size and size distribution. To our knowledge this is the first time that MEKC has been applied to the characterization of high molecular weight copolymer systems.