This paper describes mixed gas systems of SO2 and NO2 which are the essential corrosive gases in an ordinary atmospheric environment of electronic parts. It describes the corrosion product compositions and the behavior of copper in mixed and separate gases. Results of our tests show the following: (1) The weight of corrosion products with the SO2-NO2 mixed gas approximate the sum of those with the individual gases, however, the corrosion products of SO2 are affected by NO2. (2) Tests of the SO2-NO2 mixed gas closely simulates tests of electronic parts in the ordinary atmospheric environment.