Background: Making informed decisions in medical research or applications are important for both daily life and professional life of medical researchers. Knowing about nature of science (NOS), as a part of biological literacy, is a component of informed decision making, since knowledge about nature of science is needed to be aware of pseudoscientific, dogmatic and inappropriate situations out of scientific approaches in medical research and applications. For example; making a decision about using an application to cure some diseases requires knowing about multidisciplinary nature of the problem and evaluating the nature of evidence on the application suggested by the literature. There are some studies focusing on NOS understandings of different groups of students, but there is a need to investigate NOS understandings of students by considering higher levels of education (graduate level) including medical graduate education and discipline specify of NOS aspects. Objective : This study purposes to investigate understandings of medical graduate students about the aspects of nature of science. Method: The study was a case study involving four participants studying on their MS research topics in medical sciences. The study was conducted by using questionnaire of definitions and VNOS-C as data collection tools. Data collection took two months, the interview was done after the analysis of answers to questionnaire of definitions. Results: According to the results, medical graduate students showed many misunderstandings about “universally accepted one way to do science”, “objectivity”, “tentativeness”, “social and cultural embeddedness” of scientific knowledge”, “creativeness and imagination in science” and “hierarchical relationship among hypothesis, theory and law and definitional differences of them”. Conclusion: In conclusion, the participants do not have sufficient understandings to overcome problems on which making informed decisions is needed. In this manuscript, the results of the study will be described and limitations of the study and important points for further research will be explained.