Using the Xishuangbanna tropical rain forest and the Ailaoshan subtropical evergreen broad-leaved forest as the research objects,the PWS100 was used to obtain visibility data for the two forest types.Based on the visibility data of the two types of forest,we quantitatively studied the fog characteristics.The results showed that:(1) In 2014,the number of foggy days in the Xishuangbanna tropical rain forest was 196 d,accounting for 53.7% of the whole year.The number of foggy days in the subtropical evergreen broad-leaved forest in Ailaoshan was 100 d,accounting for 27.4% of the whole year.The number of foggy days in the rain forest was almost twice that of the subtropical evergreen broad-leaved forest;(2) The rainy season and the dry season in the tropical rain forest accounted for 28.06% and 71.94%,respectively.The subtropical evergreen broad-leaved forests accounted for 72% and 28%,respectively.(3) The time of generation and dissipation of fog within the tropical rain forest had certain regularity.Generally,the fog formed at night and dissipated the next morning,the longest time of one day's fog was 10.5 h.The fog generation and dissipation time of subtropical evergreen broad-leaved forest was indefinite,and the maximum duration of fog in one day reached 24 h;however,the frequency of fog was lower than that of Xishuangbanna.There were obvious differences between the two types of forest in the annual fog days.The quantitative assessment of the fog characteristics of the two types of foggy forest ecosystems could provide data in support of future climate change effects on the exchange of carbon and water in different forest ecosystems.