The Thai language is an isolated language, so it has no conjugation. Accordingly, compounds are given a great deal of weight on word formation. Highly productive compounds among the compounds of the Thai language are compounds that are made by caj being combined with other independent morphemes. The frequency of the caj compounds being used in daily life is relatively high. But a considerable number of caj compounds are more of psychological verbs related to mental operation or psychological state, so it is not easy for foreign language learners to grasp and understand their accurate meanings. This research is to analyze and describe morphological characteristics and semantic contents of caj compounds of the Thai language. The research results show that caj of the Thai language is combined with diverse words in the morphological aspect so as to have properties of noun, verb, or adjective and can function as subject, object, or predicate in a sentence. In the semantic aspect, caj compounds were described by dividing them into positive expressions and negative expressions based on the semantic contents, and they each were classified into the group of 16 words. And the caj compounds vocabulary groups were described by dividing them into antonym relations, synonym relations, and the semantic contents of caj compounds could be more systematically grasped. The results o f this research will contribute to establishing the vocabulary structure of psychological verbs of the Thai language and to explaining part of the mental world of Thai people. And it is expected that they will enhance the efficiency of Korean learners of the Thai language and provide basic data needed for comparative studies of the Korean language and the Thai language or for the development of studying materials and, by extension, future researches on lexical fields.