The textbook is the most fundamental and objective tool used by teachers and students in schools for the purpose of learning. The textbook writer is required to organize the content so that it can be logically understood by selecting the main concepts of the educational process. Studies so far have displayed restrictions in emphasizing the relationship and importance between concepts by merely providing the frequency and repetition of different concepts in a quantitative manner. Thus, this study has analyzed the life science unit of middle school science textbooks used in the 2009 revised educational curriculum in terms of the conceptual network by publishers. The middle school science textbooks published by three publishing companies were analyzed. The conclusion of this study is as set forth below. 1) There is a difference in terms of the number of concepts and network structure between publishers and units. 2) Second, the structure of the network of concepts was complex. 3) Third, the central concept of each unit varied based on the publisher. Based on this study, it is expected that the number of concepts in each unit of the new textbook will be reduced to form a simplified conceptual structure and a network that is connected to their related concepts. Furthermore, it is anticipated that this study will be helpful in the selection of textbooks that suit the characteristics of the students by adjusting the number of concepts proposed by each unit, irrespective of the author writing the unit.