N-o-nitro-phenyl- or -naphthyl-N'-halogensulfonyl ureas which may be substituted in their aromatic rings by a further nitro group (and the phenyl ureas also by fluoro, chloro, bromo, lower alkyl, lower alkoxy, trifluoromethyl, cyano or phenyl) are obtained by reacting the corresponding o-nitraniline with fluoro- or chlorosulfonylisocyanate. The products can be hydrolyzed to yield the corresponding nitroaryl ureas.