(Fe3O4)1-x-(SiO2)x composite films have been prepared by reactive sputtering iron and SiO2 targets in Ar+O2 mixture at room temperature. Transmission electron microscopy bright field images show that with the increase of SiO2 addition, uniform Fe3O4 grains are well separated by the amorphous SiO2 matrix, forming a well-defined granular structure. Temperature dependence of resistivity ρ(T) indicates that the electron tunneling mechanism featured by dominates the transport properties of the films, which smears out the Verwey transition intrinsic to Fe2/1log−∝Tρ3O4. This tunneling transport of electrons causes a spin-dependent magnetoresistance (MR){ρ(H)-ρ(o)/ρ(0)} of about-4.7% for Fe3O4 films, and-1.8% for (Fe3O4)0.6(SiO2)0.4 composite films under 46-kOe magnetic field at room temperature. Magnetic and magnetoresistance measurements reveal that the antiferromagnetically coupled Fe3O4 grains are decoupled and show the behavior of superparamagnetism at. 4.0≥x