Hydrolysis rates in aqueous acid up to 7M and at 25 °C are reported for six oxaziridines bearing various N-alkyl- and either aryl- or alkyl-C-substituents. The major reaction products are also identified. With earlier data, these results show that the extent of acid-catalysis is overwhelmingly determined by the structure of the N-alky substituent (tertiary > secondary > primary) irrespective of the hydrolysis pathway, which is influenced by both N-and C-substituents. The kinetic acidity dependences confirm that some oxaziridines may undergo concurrent protonation at both O and N atoms, with N-conjugate acid formation being more extensive for compounds with primary than for those with secondary or tertiary alkyl-N-substituents. Generally, the products arise from hydrolysis of the O-conjugate acid, but for compounds bearing C-aryl substituents hydrolysis of the N-conjugate acid is also important. The influence of N-alkyl substituents on conjugate acid formation is not related to the usual electronic interactions, but can be rationalised by steric inhibition to solvation of the N-conjugate acid. Calculations suggest that the basicities of oxaziridine O and N atoms are closely similar.