This study was aimed to define the unique characteristics of subject matter in biology , and they could be distinguished from other subject matters, such as physics, chemistry, and earth science. The characteristics of subject matter in biology could be defined by experts of biology education using consensus Delphi, They were defined in 3 domain areas:『Structure of Knowledge』,『Inquiry Method』and『Educational Objectives』. Experts consisted of 11 university professors and 4 doctors in biology education and 7 biology teachers. The consensus Delphi study was carried out in three steps. A wide range of opinions regarding characteristics of subject matter in biology was classified by 3 domain areas at the beginning. The responses by experts were analyzed and classified and the validity was examined by these experts. Twenty six characteristics in 3 domain areas were summarized and the second and third survey for the Delphi study were performed consecutively. The characteristics of subject matter in biology were finally chosen after the third survey. In the domain of『Structure of Knowledge』, 5 items of ``bioethic characteristics``, ``diversity``, ``exceptional explanations about phenomena``, ``property of academic integration`` and ``property of social culture`` were chosen. In the domain of『Inquiry Method』, 6 items of ``observation-centered inquiry``, ``inductive inquiry``, ``various controlling variable``, ``life-centered inquiry``, ``exceptional results`` and ``bioethic inquiry`` were chosen. And 3 items of ``integrated thinking ability about life phenomena``, ``understanding about life phenomena`` and ``developing ethics`` were consented in the domain of『Educational Objectives』. The characteristics of subject matter in biology defined by this study could be reflected as design and content elements needed to develop teaching and learning programs in biology. They will also provide very useful guide line for evaluating the developed teaching and learning programs in biology.