The fragmentation of O-ethyl N-1-adamantylphosphoramidothioate (1a) and its oxygen counterpart 1b was examined in ethanol at 65–100°C. The solvent hydrogen effect k EtOH /k EtOD and kinetic nitrogen effect k 14 /k 15 were determined at 80°C. The rates and parameters of activation of ethanolysis of 1a and 1b are slightly different. The solvent effect k EtOH /k EtOD was found to be equal to 0.84 ± 0.05 for 1a and 0.83 ± 0.04 for 1b. The nitrogen effect k 14 /k 15 was found to be sensitive to replacement of sulfur by oxygen, and equal to 1.0083 ± 0.0004 for 1a and 1.0065 ± 0.0006 for 1b. The data indicate that proton transfer from the OH group to the amine moiety precedes the PN bond breakage. The kinetic nitrogen isotope effect for the amine elimination recalculated for the pre-equilibrium step is equal to 1.0232 for 1a and 1.0215 for 1b. These results are consistent with the intermediacy of ethyl metathiophosphate in the solvolysis of 1a.