Heparin affinity chromatography is a well-known tool for protein separation, especially of antithrombin.  For that reason, this work was intended to propose ferromagnetic Polyethyleneterephthalate (Ferromagnetic-PET), a matrix developed in our lab, for heparin immobilization. PET film was converted to PET-hydrazide powder by methanolic hydrazine hydrate and magnetized by thermal co-precipitation method using ferric and ferrous chlorides. Heparin was activated via carbodiimide and N-hydroxysuccinimide for subsequent coupling to the magnetic support. Then the derivatives were washed ten times with distilled water by using a magnetic field. The amount of immobilized heparin was calculated by the difference between the offered quantity and that found in the supernatants using the methylene blue binding assay. The immobilization yield was about 30μg of heparin per mg of Ferromagnetic-PET. Elemental analysis for carbon, hydrogen, nitrogen, and sulfur was carried out. However, the latter could not be detected in the derivative, maybe due to the detection limit of equipment, given that sulfur constitutes approximately 11% of heparin mass. This analysis also showed 35.85% carbon and 6.03% nitrogen, which compared to those of the bare support (36.30% carbon and 7.99% nitrogen) presented a considerable increase in the molar ratio of carbon to nitrogen (1.3). Based on calculation from this increase, it is presumed that heparin was in fact immobilized once that heparin presents a ratio of 10. Infrared spectra showed bands at 1653 cm^-1 (amide I) and 1547 cm^-1 (amide II) which are characteristic of amide bond that should be originated by heparin coupling to the matrix. Furthermore, the NH₂ stretching vibration (3320 cm^-1) from support hydrazide was absent after heparin immobilization. The PET-hydrazide also present bands at 1605 cm^-1 and 1545 cm^-1, however with different intensities. The derivative containing heparin showed higher capability to adsorb methylene blue than the bare support. Collectively these results corroborate the successful of heparin immobilization and at the moment this derivative are being tested for protein affinity separation.