A theoretical study was conducted to determine the ionization constants of N-substituted amino acid derivatives using HF, DFT, and MP2 calculation methods. The extent of compatibility of these methods was determined by discussing the theoretical variables calculated in the three methods mentioned above, the relationship between the calculated physical variables have been found to be theoretical and to determine their nature. These variables were then correlated with the known chemical values of amino acids as pKa ionization parameters. The results obtained by this relationship were found to be good. This is indicated by the results of the statistical analysis across the correlation coefficient values. The theory that gave the best agreement between the values of the theoretical and the experimental ionization parameters were the MP2 method with good correlation coefficient (0.997) and standard error (0.162). As well as the large overlap between pKa values calculated theoretically with practical values where the difference (0.008) gives the opportunity to apply these variables in other studies