Silica-coated magnetic microspheres present a promising candidate for applications in bioseparation, drug delivery, and catalysis. In this paper, we report on the synthesis of core-shell structured Fe3O4/SiO2 microspheres via a modified Stober process. The magnetic composite microspheres exhibit superparamagnetism, high saturation magnetization, and good dispersion. The samples were characterized with XRD, FTIR, TEM, and VSM techniques, and further tested as adsorbents for purification of genomic DNA from Aspergillus niger NA1003 cells. The purified genomic DNA was analyzed by agarose gel electrophoresis and examined by polymerase chain reaction (PCR) amplification. The magnetic isolation protocol presents genomic DNA with PCR-ready quality and shows superior to the conventional phenol-chloroform extraction. (c) 2013 Elsevier B.V. All rights reserved.