The present study focuses on the plant naming system in the Thai language based on 1) Brent Berlin’s general principles of categorization of plants and animals in traditional societies (Berlin, 1974, 1992) which suggest that it is worthwhile to think about a plant taxonomy system on the basis of plant names since the names provide the valid key to folk taxonomy and 2) Lakoff’s central guiding principles of cognitive linguistics (Lakoff and Johnson, 2003 and Lakoff, 1987). Data on plant names collected from printed materials are selectively analyzed. The study examines the linguistic structure, folk taxonomy and conceptualization of plant terms in the Thai language. It is found that there exists in the Thai language a complex and practical plant naming system establishing a relationship between language, cognition and culture.