A nitrate-citrate-silica gel was prepared from metallic nitrates, citric acid, and tetraethoxysilane (TEOS) by sol-gel process with different pH value, and it was further used to synthesize Ni0.5Zn0.5Fe2O4/20wt.% SiO2 nanocomposites by auto-combustion. The effect of pH on the magnetic and dielectric properties Of SiO2/NiZn ferrite was studied by electron paramagnetic resonance (EPR), superconducting quantum interference device (SQUID), and impedance analyzer measurements. The pH in the starting solution affects the polymerization of TEOS, the dipole-dipole interactions existing among the NiZn ferrite, and then determines the particle size. Further, varying the pH has a direct effect on the EPR parameters (Delta Hpp and T-2), SQUID parameters (M-s, M-r, and H-c), and dielectric properties (dielectric constant and loss) of the as-synthesized powder. (C) 2005 Elsevier Ltd. All rights reserved.