A magnetically recoverable biocatalyst has been effectively prepared through the immobilization of α-amylase onto the Fe3O4 nanoparticles. The magnetic nanoparticles (MNPs) were synthesized by a sol–gel method in an aqueous system. The MNPs’ surfaces were modified with sodium silicate and 3-aminopropyltriethoxysilane (APTS). The adsorptive immobilization of α-amylase was attempted onto the APTS–SiO2–Fe3O4 nanoparticles. The physicochemical properties of the biocatalysts were characterized with Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermal gravimetric analysis (TGA). The magnetic properties of the biocatalyst were analyzed by a vibrating sample magnetometer (VSM). The activity of free and immobilized α-amylase was also evaluated by direct measurement of the absorbance of starch solution at 620 nm using UV-vis spectrophotometry. The prepared particles exhibited superparamagnetic behavior at room temperature. The mass saturation magnetization (Ms) of the bare Fe3O4 nanoparticles and the biocatalyst was 175.7 and 50.4 emu g−1 respectively. A biocatalyst was produced with a loading capacity of α-amylase of about 235 mg g−1. The enzymatic activity of the immobilized enzyme was 882 U g−1 which is about 79.53% of the free enzyme activity when not involved in the immobilized system. The immobilized enzyme exhibited significant thermal stability (stable up to 70 °C) and good durability (recycled 3 times without any obvious loss of enzymatic activity). This synthetic method provides a possible industrial route for the use of enzyme catalysts which eliminate the high operational costs and complicated recycle/reuse problems in the conventional enzyme catalysis process.