Recent research into the structure and properties of proteins and peptides as physiologically active diet components has spurred a new interest in the isolation and investigation of bioactive peptides of animal, plant and microbiological origin. The isolation and separation of protein and peptide mixtures requires advanced procedures. It usually involvesa multi-stage separation process on chromatographic columns with various packing. Immobilised Metal Ion Affinity Chromatography (IMAC) is frequently used in the complex processof obtaining peptide fractions. Affinity Chromatography (IMAC) relies on the specific interactions between amino acids, their reactive groups in proteins and peptides and „transitory” metal ions, in particular Cu2+. Those ions are immobilised by the chelating compoundon the bed, forming specific adsorbents which bind proteins and peptides. The aim of this study was to determine whether o-phosphoserine (OPS) can be used for the immobilization of copper ions on Sephadex G25 during the separation of peptidesand proteins isolated from string beans. Frozen pods of dwarf, green-podded string bean cv. Fana were used in the study. Peptide were extracted from well-homogenized string bean pods with tris-HCl buffer (pH 7.5), from which high molecular weight proteins were isolated with methanol, acetone, 20% trichloroaceticacid and the Magnafloc M-22S cation flocculant. The protein and peptide contentof the separated fractions was determined. The peptide content depended on the type of extract from which high molecular weight proteins were isolated. The results obtainedby using OPS as a chelating agent in the separation of string bean can be recommended for analysis of plant peptides.