Phenyl nitroxide radicals were obtained by UV irradiation on phenyl hydroxylamine-dioxane solutions containing oxygen gas. ESR parameters determined from analysis of these spectra were very close with the only exception in the case of methyl proton hyperfine splitting AH (CH_3) in all tolyl nitroxide radicals. Hyperfine splittjng of methyl proton o-, m-, and p-tolyl nitroxide radicals were 1.98, 0.97, and 3.02 G respectively. Such nonconstancy between the hyperfine splitting of methyl proton in o- and p-tolyl nitroxide radicals is an very interesting result and it may be explained by the steric interactions between NO group including unpaired electron and methyl group out of phenyl plane.