This experimental case study focused on pre-service science and mathematics teachers' epistemological understanding of science and how they define the concept of "science". A total of 75 pre-service teachers participated and were engaged in different contextualized and de-contextualized nature of science (NOS) activities in courses through one college semester. Qualitative data were collected via an open-ended questionnaire (VNOS-C, Form-C -Lederman, Abd-El-Khalick, Bell, & Schwartz, 2002), and a concept map which was constructed by the researchers using the participants' definitions of "science". The participants' responses to the VNOS-C were categorized as "naive", "emergent" and "informed". Furthermore, a chi-square test was used to compare the percentages of categories for the pre- and post-instruction views. The results indicated that, there was a positive change in the views of both groups of pre-service teacher regarding the aspects of NOS, with the most significant positive changes being observed in the aspects of tentativeness, subjectivity, social and cultural embeddedness, creativity. It was also observed that the pre-service science teachers were more informed about epistemology of theories and laws and scientific method than the pre-service mathematics teachers. The results of the current study revealed that the activities that are conducted using an explicit reflective approach play a positive role.