The aim of this paper is to critically review the curriculum and the contents of complex sentence in high school grammar textbooks. Furthermore some improvement directions will be proposed, if possible. The main points can be summarized as followings. Firstly, some textbooks do not reflect the intention of curriculum changes enough. Secondly, some grammatical terms, such as sentence, clause, complex sentence, predicate clause, coordination, and adverbial clause etc., should be adjusted to fit in linguistic phenomena and to analyze linguistic expressions coherently. Lastly, another change in curriculum and textbook writing is undergoing. So, before regularizing the contents of textbooks, critical reflection must be taken.