The thicurea derivatives have two active sites of both sulfur and nitrogen atom to be attacked by electrophile of nitrosonium ion (NO$^+$). We have found that treatment of thiourea derivative with dinitrogen tetroxide afford the corresponding disulfide or thiourea-S,S-dioxide. 1,3-Dicyclohexylthiourea reacts with dinitrogen tetroxide in dry acetonitrile under the nitrogen atmosphere to give 1,3-dicyclohexylthiourea-S,S-dioxide as major product. The reactions of cyclic thioureas such as 2-mercaptobenzimidazole, 2-mercaptopyrimidine, 2-mercaptobenzothiazole, 2-mercaptobenzoxazole, 6-ethoxy-2-mercaptobenzothiazole and 4,6-dimethyl-2-mercaptopyrimidine with half equimolar amount of dinitrogen tetroxide give the corresponding disulfides quantitatively in dry acetonitrile under mild conditions. Interesting reactions appear to proceed via the initial S-nitrosation by an attack of nitrosonium electrophile, and then a nucleophilic attack of sulfur atom of the remained substrates. Thus, dinitrogen tetroxide was found to be an excellent oxidizing agent for the synthesis of disulfides of heterocyclic compounds.