In Thailand, Karen is the largest hill tribe. Since ancestral time, they have been employing wild plants from the forests for their subsistence, especially for food and medicine (Trisonthi and Trisonthi, 2009). Most Karen villagers maintain traditional knowledge of medicinal plants that they use for first aid remedies, to treat cough, cold, fever, diarrhea and some simple ailments. Because of the fragmented distribution of the Karen population in northern Thailand, it is a challenge to study the shared cultural elements of the Karen's medical plant knowledge. We here document the traditional medicinal plants used by the Karen in 14 villages in Chiang Mai province, Thailand. We also attempt to determine the similarities in medicinal plant practice and the culturally important plant species between 14 Karen villages. Culturally important species are those that used by a large number of people for the same category of medicinal use (Heinrich et al., 1998).