Glow discharge optical emission spectroscopy (GDOS) is a method to analyse the optical emission of elements during sputtering of a solid, providing data on the light intensities of the elements YS. the sputtering time. By correcting the measured light intensities with standard samples, it is possible to obtain the quantitative depth profile up to about 100 pm. In the present research, GDOS was applied to the diffusion measurement of impurity atoms in metals and alloys. After a thin film of copper was coated on iron and steels, the surface film was diflused into the matrix at high temperatures. The penetration curves of copper from the surface were obtained from the GDOS data. Diffusivities of copper in ferritic and austenitic regions of iron were determined from the penetration curves, which were in agreement with previous results. D i h i o n of copper in commercial ferritic and austenitic stainless steels was also examined. The difisivities obtained were comparable with those expected from the temperature dependence of the difisivities in the ferritic and austenitic phases of pure iron.