The purpose of this study is to identify which biological concepts overlap with those in ``Physics Ⅰ,Ⅱ``, ``ChemistryⅠ,Ⅱ``, and ``Earth ScienceⅠ,Ⅱ`` developed for high school students, and to determine how the overlapping concepts help or interrupt students` learning. Overlapping concepts were identified through a questionnaire given to 12 students who had taken all of the science subjects and by analyzing the science textbooks. Another questionnaire was developed regarding the students` perception of the overlapping concepts. It was given to 37 high school students and 40 college students. 32 students from the total number of subjects were selected for interviews in an effort to grasp the meaning of students` responses in detail. The findings revealed that some of 17 biological concepts identified to be overlapped helped the students learn, as they complemented each other by explaining different aspects of the concepts. On the other hand, students` learning was interrupted by other overlapping content which was described or explained differently in different science subjects. The results of this study of overlapping concepts have educational implications regarding curriculum development and science instruction.