A total of 9 and 10 representative structures have been located on the potential energy surfaces (PES) of protonated and deprotonated glycinamide, respectively, to investigate the acid-base behavior of neutral glycinamide employing the B3LYP/6-311++G** level of theory. In the protonation processes, the proton affinities (PA) and gas-phase basicities (GB) for the three active sites, that is, the carbonyl oxygen, amide nitrogen, and amino nitrogen, have been studied. The global minimum is characterized by an intramolecular H-bond formed between the carbonyl oxygen and one of the hydrogen atoms at the amino nitrogen site, which is consistent with Most protonated amino acids. The favorable protonation site is the amino nitrogen atom followed by the carbonyl oxygen and the amide nitrogen atoms. The calculated PA for the global minimum of neutral glycinamide, 216.81 kcal/mol, is in good agreement with the experimental value (217.73 kcal/mol), indicating that glycinamide behaves as an amino nitrogen-base in the gas phase. For the deprotonation processes, the losses of protons at three possible sites, that is, the amide, amino, and carbolic hydrogen atoms, have been considered, respectively. Similarly, the global minimum is also characterized by an intramolecular H-bond formed between the amide nitrogen atom and one of the hydrogen atoms at the amino site, which is further confirmed by higher-level calculations, such as MP2, MP3, MP4(SDQ), and CCSD(T) levels, including full electron correlations. The relative order in the calculated PAs and GBs of the three sites for the deprotonated glycinamide is N3 > C2 > N4, indicating that glycinamide behaves as an amide nitrogen-acid in the gas phase. Additionally, temperature and solvent effects on the protonation and deprotonation processes have been discussed qualitatively.