While elemental sulfur has been largely used as oxidant or sulfurating agent, its role as a catalyst has not been developed. We report here its catalytic activity in the oxidative condensation of o-phenylenediamines with acetophenones in DMSO to provide quinoxalines. The method was also extended to a-tetralones, propiophenones (R = Me) as well as higher homologues (R = Et, n-Pr) in place of acetophenones, leading to a wide range of naphthoquinoxalines and 3-substituted 2-arylquinoxalines.