Abstract: Using observed fog and haze data from 567 stations during 1971-2010 in China, the general distribution and the seasonal and decadal variations of fog days and haze days were demonstrated. A rotated empirical orthogonal function was used to classify the fog days in China according to climate. The results show that: (1) Fog days were distributed mainly over the southeastern coastal area, the Sichuan Basin, the border between Hunan and Guizhou, the Shandong coastal area, and southern Yunnan. Haze days were concentrated over North China, Henan, the Pearl River Delta, and the Yangtze River Delta area. (2) Seasonal variations appeared: The numbers of fog days and haze days in autumn and winter are larger than those in spring and summer. (3) Fog days and haze days in China exhibit obvious decadal variations. There are more fog days from the 1970s to the 1990s, and fewer from the 1990s to 2010. The yearly variation trend of haze days was ascending rapidly from 2001. (4) The entire area of China can be divided into 10 parts. The north China, Sichuan, Chongqing, and the middle and lower reaches of the Yangtze River areas are major fog regions.