The effect of Co inserted layer with thickness below 20 nm on the dielectric permittivity of SiO (60 nm)/Co(x nm)/SiO (60 nm) thin films fabricated on glass B270 substrates by the reactive sputtering technique was studied. The dielectric constant is around 7.4 for B270 glass substrate and SiO /B270 film. However, it is rapidly raised up to roughly 55 for all the SiO /Co/SiO samples with the thickness of Co inserted layer larger than 2 nm. From the cross section TEM pictures of the SiO /Co/SiO films with 1 and 2 nm Co thickness, we have experimentally demonstrated that this enhancement behavior of the dielectric constant is due to the growth mechanism of the Cobalt inter-layer from island clusters to continuous Co layer for samples with x larger than 2 nm. The adding of a Co inter-layer redistributes the interface charges between Co and SiO layers, and that enhances both the intrinsic polarization and its dielectric constant. For the magnetic induced dielectric variation, the variation of the dielectric constant also increased with thickness of Co for samples with x larger than 2 nm. A direct observation of a 0.04–0.20% dielectric variation is induced by external magnetic field. However this increase behavior is roughly saturated for applied magnetic field roughly above 60 Oe. The magnetodielectric properties in SiO /Co/SiO films are manifested and it has potential for a ferroic sensor application.