Effects of the pH and temperature on the magnetic properties of Ni0.5Zn0.5FeO4/SiO2 nanocomposites have been studied by electron paramagnetic resonance (EPR) technique. Particle size of these composites was calculated from Scherrer's formula and transmission electron microscopy (TEM), and that increased with increasing pH value. The peak-to-peak linewidth (DeltaH(pp)), g factor and spin number (N-S), measured at room temperature, increased with increasing pH value, while the spin-spin relaxation time (T-2) decreased. Furthermore, these parameters (DeltaH(PP), g factor, N-S and T,) were measured as function of temperature. The DeltaH(PP) g factor and N-S decreased with increasing temperature, whereas the T, increased. (C) 2004 Elsevier B.V. All rights reserved.