Magnetic nanobeads are more and more widely used in the fields of biology and medicine. However, there are still some shortcomings about the magnetic nanobeads such as nonuniform size, poor dispersity, weak magnetism and low functionalization degree after modification. This study was focused on how to acquire magnetic nanobeads by overcoming these drawbacks. Firstly, a highly magnetic nucleus with homogenous sizes, Fe₃O₄, was prepared. Then, it was successively modified by tetraethoxysilane and 3-aminopropyltriethoxysilane, giving functionalized magnetic nanobeads Fe₃O₄@SiO₂ or Fe₃O₄@SiO₂—NH₂, respectively. The influence factors on magnetism, dispersity and functionalization degrees were further studied. Rusults: Fe₃O₄ could be stable for 8 d in EtOH and exhibit a strongest magnetic strength of 56 eum/g, when prepared at room temperature under ultrasonic condition with the amount of ammonia (1 mol/L) for 50 mL. When the amount of TEOS was 0.5 mL, Fe₃O₄@SiO₂ could be prepared and stable for 12 d in EtOH with a strong magnetic strength of 30 eum/g. When functionalized in toluene at 70 ℃, Fe₃O₄@SiO₂—NH₂ could be prepared and stable for 14 d in EtOH with a still strong magnetic strength of 25 eum/g. Moreover, it reached a biggest NH₂ group grafting degree of 2.306 mmol/g, which was higher than that reported in the literatures. In a word, both of these modified magnetic nanobeads show better dispersity and still strong magnetism. And above all, they bear active hydroxyl or amino groups on their surfaces, which make them easier to bind with organic molecules and so better for applications in the fields of biology and medicine.