Abstract: There is currently great interest in the chemistry of nitric oxide (NO) following many important discoveries showing that NO is involved in a range of human physiological processes.¹ Among ocean of researches in this area, some attention has been paid on the release of NO from aromatic N-nitrosoureas,not only from the point of view of their potential therapeutical use as alternative NO-releasing drugs,² but also with regard to their possible involvement in vivo as potential NO-storage and transport vehicles.³ Thus, the cytoxicity mediated by NO is expected to be potent in aromatic N-nitrosoureas having NO-releasing ability. For NO-donor compounds, homolytic cleavage energy of N-NO bond (ΔHhomo) is considered a good measure of their NO-releasing ability. Here, we provide a method to derive the ΔHhomo data and present some results showing structure influence on the N-NO bond strengthes for several series of disubstituted ureas and thioureas.