The ring opening of β-sultam via an H_ 2 O-assisted ammonolysis process was studied by using Density Functional Theory(DFT) method at the B3LYP/6-31G* level as a further step in the theoretical investigation of the ammonolysis reaction of β-sultams. The calculated pathways are analogous to those previously described for the non-assisted ammonolysis reaction. Solvent effects were assessed by using the polarized continuum model(PCM) method. The results show that mode 1 and pathway a in channel Ⅱ are the most favorable ones in both the cases. The energy barrier of the cleavage of C—S bonds producing P1 is the highest among all the energy barriers. The presence of a solvent in the continuum model disfavors the reaction, whereas the participation of water in the ammonolysis reaction plays a positive role and reduces the active energy greatly. The relative energies of all the transition states in the assisted ammonolysis are 20—80 kJ/mol lower than those for the non-assisted reaction. The ring opening of β-sultam via an H 2 O-assisted ammonolysis process was studied by using Density Functional Theory (DFT) method at the B3LYP / 6-31G * level as a further step in the theoretical investigation of the ammonolysis reaction of β Sultans. The calculated pathways are analogous to those previously described for the non-assisted ammonolysis reaction. Solvent effects were assessed by using the polarized continuum model (PCM) method. The results show that mode 1 and pathway a in channel II are the most favorable ones in both the cases. The energy barrier of the cleavage of C-S bonds producing P1 is the highest among all the energy barriers. The presence of a solvent in the continuum model disfavors the reaction, the the participation of water in the ammonolysis reaction plays a positive role and reduces the active energy greatly. The relative energies of all the transition states in the assisted ammonolysis are 20-80 kJ / mol lower than those for the non-assisted reaction .