An improved approach for preparing amino-modified magnetic nanogels has been developed in this paper. Polyallylamine magnetic nanogels (PAA-MNGs) were synthesized in one step by photoinitiation and ,in situ, photopolymerization of allylamine in Fe,3,O,4, aqueous suspension under UV irradiation. Morphology, mean diameter and diameter distribution of the PAA-MNGs were measured by TEM and PCS respectively, while the magnetite content was confirmed by TG and the superparamagnetism identified by VSM. Biomolecules, such as proteins, can be coupled to the surface of PAA-MNGs in virtue of amino groups. Streptavidin-coated magnetic nanoparticles (SA-MNPs) were prepared by covalent immobilization of streptavidin (SA) activated by 1-Ethyl-3- (3-dimethyllaminopropyl) carbodiimide hydrochloride (EDC) and N-hydroxysuccinimid (NHS) on PAA-MNGs. The biotin binding capacity of SA-MNPs was proved by colorimetric measurements using the probe biotin p-nitrophenyl ester (BNPE). Therefore, PAA-MNGs may be a suitable vehicle to carry biomolecules for applications in many areas of biotechnology.