To improve the concept mapping method for meaningful construction of biology knowledge, this study analyzed biology contents of middle school science textbooks. This study aimed to identify the sentences or the propositions which cause difficulties in concept mapping from the biology contents of middle school science textbook. And their distributions were also investigated. Analysis was concerned about ``the sentence which contains many propositions`` and ``the proposition which contains adverbial phrase or clause`` which were pointed out causing difficulties in concept mapping from the previous studies. In most middle school biology units, more than 38% of the sentences contain two or more propositions. Extracting scientific propositions from complex sentence is too difficult for the students who faced a new scientific knowledge just now. It makes most students to feel difficulties in concept mapping. Thus, the students need to be given the simple form of knowledge, or guided in the procedure of extracting propositions from the complex sentence. And adverbial phrases or clauses are frequently used in middle school biology contents (81.2%). So, it seems that the newly suggested concept mapping method which allows the sublinker to represent adverbial phrases or clauses is highly required for solving the difficulties in concept mapping. Biology knowledge that students are usually confronted with, has various sentence structure and complex morphology. So there are many difficult patterns of knowledge expression to construct concept map with traditional method, like the difficulties in concept mapping some knowledge about concept`s definition that denoting a scientific phenomenon or process. Thus investigations about concept mapping method for solving these difficulties should be continued for the students` effective using of concept map in biology learning.