The solubilities at 298.15 K of glycine and its oligopeptides (glycylglycine, triglycine, tetraglycine, pentaglycine, and hexaglycine) in aqueous solution at various pH values and concentrations of NaCl, PEG 6000, and ethanol are reported. At high and low pH, the solubilities increase remarkably. The solubilities generally decrease with an increase of the concentrations of ethanol and PEG 6000 in the experimental range, which indicates that ethanol and PEG 6000 can be used as an antisolvent or precipitant for the precipitation and crystallization of glycine and its oligopeptides. As the NaCl concentration increases, the solubility of glycine first decreases and then increases, while the solubilities of glycylglycine and triglycine increase monotonically with the NaCl concentration.