Corrosion data of 12 years of atmospheric exposure of five types of stainless steel at six sites in China were obtained. The exposed steels are of commonly used stainless steels. The test sites cover typical environments of temperate and subtropical, industrial, marine and rural. Generally, stainless steels are corrosion resistant in the atmosphere. Corrosion occurred mostly in the form of pitting. Of the main environmental factors that have influence on atmospheric corrosivity of stainless steels, the most influential one is Cl pollution. If high humidity and heat are combined with Cl pollution, extra high corrosion will be the result, a phenomena not being noticed before. Sulphur dioxide has very little effect on the atmospheric corrosion of stainless steels. Deposition of dust and surface defects are the main starting points of atmospheric corrosion for stainless steels. 13% Chromium content is the basis for steel to be stainless. When Chromium content is over 18% stainless steels become excellent in atmospheric corrosion resistance. Molybdenum raises corrosion resistance of stainless steels, especially in marine environments. Extra low carbon raises their corrosion resistance. Even in humid and hot marine environments of high corrosivity, the steels with extra low carbon and some molybdenum are not corroded after 12 years of exposure.