The mechanism of hydrolysis of nitroguanidine has been studied theoretically. The molecular geometries have been fully optimized at AM1 level of theory for reagent, activated and product complexes for hydrolysis of nitroguanidine in neutral, acidic and alkaline media, respectively. In neutral and acidic media, both activated complexes have four-membered ring structures, and the reaction-coordinated eigenvectors show heavy-atom reorganization and proton transfer to be truly concerted in both cases. In alkaline medium, the hydrolysis also involves activated complex. The calculated activation energies for the hydrolysis of nitroguanidine in neutral, acidic and alkaline media are 278.2 kJ/mol, 330.2 kJ/mol and 213.0 kJ/mol, respectively.