The nature of science aspects (NOS) are the most emphasized theme in many curriculum and reform attempts. Teachers as a curriculum implementer in the classroom play important role for policy, arrangements and classroom experiences on NOS understandings of students. Researchers generally assessed the teachers' NOS conceptions using open-ended questions plus interview in limited samples. However, in the literature, there have been some critics on this way of assessment. For that reason, this study aims to assess elementary science teachers' (N = 47) NOS conceptions by using "Open-ended questions" and "Knowledge test". The results showed existence of some misunderstandings on NOS and the participants' responses to knowledge test and open-ended questions gave similar pattern in terms of ten aspects of NOS, except for three aspects. (Contains 7 tables and 1 figure.)