Fe 3 O 4 magnetic nanoparticles (MNPs) were obtained using the gas condensation method. These MNPs were modified with 3 aminopropylsilane (APS) through covalent bonding. The methods of qualitative and quantitative analysis of the modified MNPs were developed using UV and IR spectroscopy and induc tively coupled plasma emission spectrometry (ICP ES). It was established that the maximum loading level of APS on the surface of Fe 3 O 4 MNPs was 0.91 mmol/g MNP. The study of the activity of the surface amino groups of the nanocomposites was carried out by the example of their modification with (S) naproxen. The optimum conditions for coupling reaction were found. It was shown that the reaction proceeded most effi ciently when using 1 ethyl 3 (3 dimethylaminopropyl)carbodiimide (EDC) as coupling agent in the pres ence of 1 hydroxy 1H benzotriazole (HOBt). The maximum immobilization level of (S) naproxen on the Fe 3 O 4 MNP surface was 0.55 mmol/g MNP. Thus, the high reactivity of amino groups of the obtained nano composites was shown, making it possible to further modify them.