Naphthoxyl radicals can be stabilized by the appropriate introduction of sterically hindered groups at the 2- and 4-positions. In this study, a new 1-naphthoxyl derivative was synthesized, and its spin density distribution and redox potential were determined. The time course of its ESR spectrum revealed that the half-life of such a radical in a degassed sealed state was 4.0 days. As a result of this study, valuable information has become available concerning the electronic structure and stabilization strategy of the naphthoxyl radicals.