Fe₃O₄@PEG have been proposed for sorption of L-lysine-α-oxidase (LO) from the culture fluid of Trichoderma harzianum Rifai F-180 for the first time. To synthesize the Fe₃O₄@PEG nanoparticles, an original method based on aqueous biphasic systems has been developed. The PEG-modified magnetite provide a high sorption ability towards LO in contrast to the non-modified Fe₃O₄ synthesized by the traditional precipitation method. The morphology and structure of the prepared nanoparticles were characterized by TEM, FTIR and XRD. The data on magnetic properties and stability in physiological media are presented. The synthesized nanoparticles ensure quantitative sorption and desorption of LO during at least 3 cycles.