To assign definitely the hyperfine coupling constants for the alpha- and beta-protons of the well-resolved spectrum of poly(styrene) radical, five types of deuterated styrenes were synthesized and polymerized in the cavity of an ESR spectrometer. Their propagating radicals which presented sufficiently high concentrations were subjected for ESR measurement during polymerization in bulk. The spectra obtained exhibited different splitting patterns depending on the number and positions of deuteration. The relevant hyperfine coupling constants for the protons and deuteriums bound to the respective terminal units of the propagating radicals were determined. As a result, the coupling constants for the alpha- and beta-protons of the poly(styrene) radical, a(alpha) = 15.90 G, and a(beta) = 18.30 and 15.90 G, were unambiguously confirmed.