Magnetic properties and electrical resistivity of Fe-Mg-O thin films produced on cooled substrates by liquid nitrogen during the sputter-deposition have been studied. The films on cooled substrates exhibit high saturation magnetizations compared to those with the same magnitude of electrical resistivities on non-cooled substrates. For example, saturation magnetization of a film on a cooled substrate, when the electrical resistivity is about 150μΩcm, is nearly 2 kG larger than on a non cooled substrate. It should be noted that the substrate cooking is also effective in increasing saturation magnetization and electrical resistivity of Fe-Mg-O thin films.