Lichen diversity was studied in areas around Mae Mo power plant during November-December 2007. Four study areas around Mae Mo power plant were selected: Ban Sop Mo, Ban Sop Chang, Ban Pang Puai and Ban Dong. Six mango trees (Mangifera indica L.) were randomly selected for lichen investigation in each site. The grid frame size of 20 x 50 cm2 was put on the tree trunk. The results showed that Ban Sop Mo, which is located near the power plant, had the lowest diversity of 2.14 while Ban Dong had the hightest diversity of 2.51. Furthermore, some species of lichen such as sterile crust lichens and genera Dirinaria picta, Chrysotrix xanthina and lichens of family Graphidaceae were found in every of the study areas. Comparing the numbers of foliose lichen with crustose lichen,the result showed that there were the numbers of crustose lichens higher than the numbers of foliose lichen in all study areas. In addition, there were bleached thallus of foliose lichens due to air pollutants such as Dirinaria picta,Hyperphyscia adglutinata, Pyxine cocoes which were found in all study areas. The highest total frequency was found at Ban Pang Puai and the lowest was found at Ban Dong.