This study aimed to explore what kinds of epistemological messages were conveyed through teacher discourse in modeling-based and traditional elementary science classrooms and how teachers framed the two classrooms distinctively through these messages. Data came from two sixth-grade teachers' science classrooms--one characterized as a modeling-based classroom and the other as a traditional classroom. Video recordings of science lessons in the two classrooms were analyzed as the main data source. Epistemological messages from within the teacher discourse in the two classrooms were identified, and different ways of the teachers' epistemological framing by these messages were inferred. As a result, we identified a constellation of epistemological messages corresponding to a variety of epistemological themes and categories communicated by the teacher in the modeling-based classroom. This constellation indicated the teacher's framing of the modeling-based classroom as supportive of students' construction of knowledge through engagement in the scientific practice of modeling. By contrast, in the traditional science classroom, epistemological messages served the teacher's framing of the classroom as a place for learning correct knowledge by recording and memorizing the information transferred via the teacher and the textbook. The findings suggest that epistemological messages can be used as a conceptual and instructional tool to analyze and shape epistemic aspects of science classrooms and that rational authority on scientific practices of modeling can be an important characteristic of a modeling-based science classroom that sets it apart from a traditional classroom.