The biocatalyst horseradish peroxidase (HRP) was successfully immobilized onto magnetic nanoparticles by the glutaraldehyde method. The influence of pH medium, ionic strength, the initial protein concentration, temperature and the effect of the functionaladditive pentaethylenehexanamine on HRP immobilization were studied. The studyconsisted in seeking for the optimal conditions at which the binding efficiency and the activity of the immobilized horseradish peroxidise were the highest. The results showed that the highest immobilization yield, nearly 60 %, was attained at pH 4.0. It was found that the variation of ionic strength directly affected the HRP immobilization. The enzymewas immobilized at the optimal conditions with the final residual activity of 80 %. However, the enzyme attached onto functionalized magnetic support and additionally coimmobilized with the functional additive, showed better hydrogene peroxide tolerance than the immobilized enzyme without the pentaethylenehexanamine, respectively.