Seven salicylaldehyde-amino acid Schiff bases in water were investigated by means of electronic spectra, which is helpful to investigate the label of radionuclides with the seven ligands in water for radiopharmaceutical study. Except 10(-5) mol x L(-1) for Sal-tyr, the minimum concentration of formation is 10(-4) mol x L(-1) for all other Sal-aas. Only Sal-his is generated at pH 9-10, while the minimum pH conditions for formation are 8 for Sal-gly and Sal-tyr, and 9 for other four. All Sal-aa but Sal-cys, whose concentration at 36 h is higher than that of newly produced one, decompose gradually since generation, with existing time of 24 h for Sal-gly and Sal-glu, and 48 h for other four.