The giant magnetoresistance (GMR) of a magnetic/nonmagnetic superlattice, which is expected to be a novel magneto sensor with a high MR ratio, has been known to be significantly affected by its deposition condition. We analyzed the residual gases during the deposition, the consequently, MR ratio of resulting films, drastically decreases with increasing residual water in the deposition atmosphere and decreasing deposition rate, which is considered to be due to the incorporation of oxygen from the residual water into the film. The GMR property is found to be universally expressed in terms of the residual water to deposition rate ratio.