Partially N-methylated polyvinylamines were synthesized by the reaction of polyvinylamine with formaldehyde in the presence of potassium tetracarbonylhydridoferrate. The degrees of methylation were determined from the NMR spectra. The values of the derivatives which were prepared in the ratios of 0.5 and 1 mole of formaldehyde to 1 mole of polyvinylamine were about 45 and 62 percent respectively. The chelations of the derivatives-cupric ion and the polyvinylamine-cupric ion were investigated with a pH variation. The chelations of the derivative systems occurred at higher values of pH than the chelation of the amino system. Also, the absorbances of the derivative complexes were smaller and the maximum absorption wavelengths of the derivative complexes were shifted to longer wavelength regions. These results can be attributable to 8.n unstable complex formation due to the steric hindrance of methyl group.