Lichens constitute an important component of tropical forest biodiversity. This study inventoried corticolous lichens and examined their variation in various forest types with varying climatic conditions in Mt. Kenya, East Africa. Specifically we evaluated variation of lichen assemblages in relation to forest types and tree diversity along an altitudinal gradient (1800-3100m). Ten study sites were established on two contrasting sides of Mt. Kenya in the indigenous forest: six of them at Chogoria which is on the humid southeastern windward side of the mountain and four sites on the Sirimon side located on the drier northwestern leeward side. Overall 242 lichen taxa were documented; with Chogoria and Sirimon forests having 148 and 94 species that translated to an adequate sampling effort of 74 % and 68 %, respectively. The two contrasting forest types (Chogoria and Sirimon) supported slightly different lichens assemblages. Meanwhile lichen assemblages were found to significantly vary with elevation (or forest types) and with tree host. Posterior analyses showed that the differences were significant among sampling sites (or forest types) on the Chogoria side and insignificant on the Sirimon side. Similarly the number of lichens differed significantly among the host tree species. This study stresses the urgent need to upscale the sustainable management of the presently threatened tropical forests in order to preserve their structural heterogeneity